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Probiotic Rich Fermented Red Onions & 10 Minute Sheet Pan Fish Tacos!

April 10, 2019

Sheet pan fish tacos topped with tangy, probiotic rich fermented red onions are a match made in heaven!

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Beach days, rock hunting, & fish tacos…

We made it. Our feet were grounded on the Lake Michigan shoreline all weekend, and we couldn’t be more full of joy! While we spend most of our spring and summer days with our feet in the soft, powdery sand of our hometown shoreline, we do love to beach hop to some special places along Lake Michigan with a more rocky landscape so that my rock hunters can find special treasures! My oldest has become quite the geologist in the last few years, with such a love for collecting different rocks and fossils. And my oldest also couldn’t think of a better way to re-fuel after our first spring beach day than fish tacos!

The obsession began a few summers ago…

We were enjoying a rare to us night out at a restaurant after a long, hot beach day, and my oldest, who was about 6 at the time, ordered fish tacos. They were just about the biggest hit you could ever dream of for her, and she still talks about them to this day. They had the avocado crema, mango salsa, and those pretty little pickled red onions sprinkled on top – the works! She was obsessed, and I just knew I had to duplicate them for our menu rotation after that!

The real deal “pickled” red onions

Quick little refrigerate pickled red onions are great, and truly is nothing wrong with them, but what if there was a way to make them the “real deal” way? Instead of pickling them in vinegar for the sour punch, letting nature do it’s work with a little sea salt and water, and allowing the natural, good bacteria in the vegetable ferment the onions to tangy perfection – the way your ancestors would have preserved and “pickled” onions! And let me tell you…the tangy, sweet, salty, crunchy red onions make *the* best fish taco topping!

A quick fermentation 101

It’s as simple as making a little salt water brine to suspend your onions, a clean, air tight space to allow the science to happen, and a little time. When you add the salt water brine to vegetables, the good bacteria in the vegetables starts eating away at the natural sugars in the veggie. The lactic acid left behind from this veggie sugar metabolizing gives the vegetable a tart, tangy taste, and is also just so amazingly good for our bodies! It is a great way to keep beneficial bacteria in our gut flora (probiotics), and it balances stomach acid.

Ok, so what do I need to get started fermenting my onions?

While you can definitely get your ferments going today with just glass jar and a plastic lid (metal lids will corrode over time so plastic is recommended), as you get going you may want to take a look at fermenting tools that make the process even easier and stress free.

Vegetable ferments do best in an anaerobic environment (that is, “no oxygen” using an air tight seal). Plastic lids work fine, though some air does get through, and as the gasses build up in the ferment you need to “release” them by opening the lid here and there. The air that gets through also makes it easier for stray airborne microbes and molds to get in which can make the whole jar go bad.

There are a couple of sealing options you can choose from, and I really have found these to give the best fermenting results. The one that I use is the first recommendation, the Pickle Pipe.

  • The Pickle Pipes & Pebbles :: I am convinced a busy, “every day” mom invented this fermenting tool! Talk about zero fuss, *easy to clean,* and affordable! The Pickle Pipe creates a seal with a simple (easy to wash!) silicone disk, and the metal ring your jar comes with. The “pipe” part of the silicone disk has a special opening that only pressures open when the gasses build up in the jar and need to be released. So basically…set it and forget it! You don’t have to check for pressure everyday at all. I also am in love with their Pickle Pebbles which weight down the ferment at the top so you don’t have to worry about molding or the tips of the veggies going bad from being out of the brine. Invaluable! I have never had a ferment go bad or mold using my Pickle Pipes and Pebbles.
  • Fido Jar :: Fido jars create an incredible anaerobic sealed environment and are super easy to clean and take care of. No crazy parts to clean, and they are beautiful lined up in the kitchen to ferment! You will need to “burp” these every day or so to let the gasses out but they work very well! They are pricier than mason jars (especially if you already have a lot of mason jars at home, and can just get some Pickle Pipes to top them off), but they will last forever and, again, they are beautiful!
  • Traditional Fermentation Crock :: I have to be honest…I love these! I really do! They are on my foodie dream list and when I can afford a really beautiful new fermenting crock I really, really want one for my kitchen! They are gorgeous, easy to clean and work fantastic. They come with a weight to keep the veggies down to prevent molding and they create a perfect anaerobic environment.
  • Air-Lock Lids :: These are a really great, inexpensive option – especially if you already have a lot of mason jars at home. I think the Pickle Pipes are easier to clean and use, but if you have some of these lying around don’t let them go to waste – they work great!

Do the kids like them?

Well, 2 out of my 3 give these little onions 2 thumbs up. My youngest is still warming up to them, but onions are strong in the first place, and probably aren’t a great fermented food to start out with for really little guys. My suggestion for littles and fermented foods is to start out with fermented carrots and sauerkraut. Sour pickles and fermented asparagus are fantastic options that are kid friendly too. I also loved this recipe for Ranch Dressing made with Kefir (a style of fermented milk) to dip your veggies in! The littles will love it, and you can feel good about what their gut being nourished. All in all, be inspired to give even the smallest of children in the house a try of fermented foods. My girls were eating small shreds of sauerkraut and shredded fermented carrots by the age of 9 months old, and developing that taste palate is priceless.

Fermented onions first, then onto the tacos!

So grab a mason jar and get some fermented red onions going! Then plan a fish taco night into your menu plan this month and just wait until you see how fun fish taco night is! Here is the recipe for the fermented onions, and the tacos will follow.

Print Recipe
5 from 32 votes

Probiotic Rich Fermented Red Onions :: The Perfect Topping for Fish Tacos, Salads, Wraps, and More!


  • 1 pint warm water
  • 2 tsp sea salt
  • 1 large red onion sliced
  • 1 tsp sugar optional


  • Dissolve the sea salt in the warm water.
  • Put the sliced red onions and sugar into a mason jar, packing them in tightly.
  • Pour the salt water brine over the onions leaving a half inch to inch of headspace at the top.
  • Add your fermenting weight over the onions in the brine to be sure the onions stay submerged. If you do not have a weight, just be sure the onions are completely submerged in the brine or you will get molding.
  • Put your fermenting lid on the jar (I use pickle pipes) and leave in a warm space in your kitchen on the counter or in a cupboard for 1-3 weeks. You can taste the onions along the way to get your preference of tartness. If your house is warmer, it will ferment faster, and if your house is cooler, it will take longer. Everyone has a different taste for fermented foods. Your fermented onions should smell oniony and taste pleasantly tangy/sour. The longer you ferment the more beneficial bacteria will be present. I ferment my onions around 3-4 weeks if it is winter time and cooler in my house, and it takes more like 2 weeks in the very warm summer months.

But getting back to those fish tacos!

A couple months back, I had dinner with some friends at a local restaurant. It was all about conversations that didn’t revolve around slime, school work, or Hatchimals; glasses of wine, and great food – it is such a necessity of mom life to do this! One of my friends and I ordered the fish tacos, and, after we quite literally devoured them, I had a renewed desire to get a fun, family friendly fish taco recipe to the blog!

Sheet pan prep for busy families

…Because fish tacos on a Wednesday night is just the bees knees, and I promise it will be *the* thing that gets you through the rest of the week. Just a quick slice through some wild caught white fish, a toss through some taco season of your liking, and 10 minutes at the most in the oven. That is weeknight dinner at it’s best.

What kind of fish?

Any wild caught white fish will do, though we have certainly enjoyed fish tacos with wild caught salmon! Use whatever your family likes to eat. We pick up wild caught mahi-mahi, cod, and salmon at Costco. We also have a local fish monger that has the fish here and there. Check around where you live, and ask! Fish mongers are always happy to tell you about where their fish comes from!

Fish Taco Bar topping ideas!

  • Shredded cabbage or lettuce
  • Coleslaw
  • Fermented Red Onions (Recipe is below!)
  • Raw cheese or goat cheese
  • Guacamole
  • Shredded carrots (or ease your littles into the fermented topping idea by using shredded fermented carrots – my youngest eats them this way)
  • Salsa
Print Recipe
5 from 32 votes

10 Minute Sheet Pan Fish Tacos



  • 4 fillets of white wild caught fish such as cod or mahi mahi Cut into strips, or bit sized chunks if you have little ones at home.
  • 3-4 tsp taco seasoning I use my own taco season mix.


  • Shredded cabbage or lettuce
  • Coleslaw
  • Fermented Red Onions (See above recipe)
  • Raw cheese or goat cheese
  • Gauacamole
  • Shredded carrots
  • Salsa


  • Preheat the oven to 400 degrees, and line your baking sheet with Silpat, or spray with avocado oil spray, or lightly grease with butter or coconut oil.
  • Toss the cut up fish with the taco season and spread the pieces of coated fish onto the sheet pan. Bake for 10 minutes. If you made smaller pieces for little kids, you will have a shorter cook time.
  • Serve on your favorite tortillas with toppings of your choice!
My sweet tween, happily inhaling said fish tacos after the photoshoot 😉

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  • Reply Kiran Dodeja Smith April 11, 2019 at 10:04 am

    5 stars
    This meal has my name all over it! I’ve been wanting to make fermented onions forever; this is giving me the push I need to try it.

  • Reply Beth Learn - Fit2B April 11, 2019 at 11:20 am

    I love my pickle pipes and pebbles! They work so well. I’ve nevee made red onions, so I’m excited to find and try this recipe!

  • Reply tina April 14, 2019 at 7:32 pm

    Yum! Those tacos look delicious – can’t wait to try!

  • Reply Tessa Simpson April 14, 2019 at 10:59 pm

    5 stars
    I am so all over the 10 minutes!! I am not a fan of raw onion, but fermenting them mellows them SO much, thanks for teaching me how to do it, yum!

  • Reply Lori April 15, 2019 at 1:39 pm

    5 stars
    We made this last night minus the cheese and salsa. So delicious!

  • Reply Kari - Get Inspired Everyday! April 15, 2019 at 4:41 pm

    5 stars
    Fish tacos are my all time favorite, and I’m extra partial to pickled onions, so I can’t wait to try your fermented version – sounds delish!

  • Reply Jean April 15, 2019 at 5:03 pm

    5 stars
    I’m love tangy fermented or pickled onions and they are so perfect for tacos!! This looks amazing.

  • Reply linda spiker April 15, 2019 at 6:06 pm

    I adore fermented onions on tacos. Great job 🙂

  • Reply Megan Stevens April 16, 2019 at 1:15 am

    5 stars
    I love the story you tell here, and how it includes this meal. That’s kind of how we do food too, all woven into being super hungry after outdoor fun, and seasonal. What great memories the girls are getting. My family will love these onions and tacos!!

  • Reply Raia Todd April 16, 2019 at 12:12 pm

    5 stars
    My kids LOVE fermented onions, and I love fish tacos! I guess this really is a match made in heaven. haha.

  • Reply STACEY CRAWFORD April 16, 2019 at 12:37 pm

    5 stars
    I’m not an onion lover and pickled or fermented is the only way I will eat and enjoy an onion. No idea why they taste so much better fermented, but they certainly do! Great recipe!

  • Reply Jessica April 16, 2019 at 1:27 pm

    Gah! This all looks soooooo tasty. And those fermented onions…yummo. Thanks for sharing!

  • Reply Hope April 17, 2019 at 12:31 am

    5 stars
    I love red onions raw, cooked or pickled but my little boy only enjoys them pickled or fermented as they are not as strong and have a nice sweetness to them. I love how easy you make this sound – these are a great topping for tacos, salads or burgers of any kind!

  • Reply Lu April 17, 2019 at 2:45 pm

    Que cantidad de agua, no entiendo que es ointa

  • Reply paleoglutenfreeguy April 17, 2019 at 2:57 pm

    5 stars
    I love pickled red onion but never thought of fermenting them! Good to know that the process is so simple! I can get a batch started this weekend.

  • Reply heather April 18, 2019 at 1:58 pm

    5 stars
    I love fish tacos! I totally need to make these red onions too, they sound lovely!

  • Reply chihyu April 19, 2019 at 10:26 pm

    5 stars
    I totally love this! Probiotic and so healthy for you!

  • Reply Susannah April 19, 2019 at 11:10 pm

    5 stars
    I’ve only just gotten started with fermenting, and these onions look fantastic! (Tacos, too!) Will be giving both a try soon!

  • Reply Anne April 20, 2019 at 2:22 pm

    This is a great recipe. I just love the fermented onions

  • Reply Annemarie April 21, 2019 at 7:01 pm

    5 stars
    I can’t wait to make these fermented onions when I get red onions from my farm share. They look amazing!

  • Reply Mimi April 21, 2019 at 10:19 pm

    5 stars
    Fantastic tacos that are so unique. And those red onions must give the dish so much flavor – yum!

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  • Reply Anna Hattrem June 19, 2019 at 11:59 am

    5 stars
    I made these fermented red onions from your recipe and I couldn’t be happier. Thank you for simplifying the fermenting process!!!

  • Reply Katie September 17, 2019 at 7:30 pm

    I’ve been meaning to try this since you posted the recipe and finally got around to it. The onions are amazing and I think the tacos are my new favorite dinner. I couldn’t find fresh mahi mahi but was pleasantly surprised how well it turned out with frozen filets. Topped with some avocado and the red onions this is even better than the fish tacos we get at our favorite Mexican restaurant. Thank you for another delicious recipe!

  • Reply Becky January 13, 2020 at 2:29 pm

    I plan to make these onions and the tacos -Yum! But my question is- Do you really use both sliced cabbage And Cole slaw ?? My experience with fish tacos has been one or the other depending on where we find and order them…? Just wondering ?? Thanks!

    • Reply Renee Kohley January 14, 2020 at 11:07 am

      Sometimes we do both! I hope you enjoy the onions!

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  • Reply Susan March 4, 2023 at 3:44 pm

    I was excited to ferment onions and finally tasted one after two weeks. It’s good! However, my concern is the mold I found on the underside of the pickle pipe (and the cloudy brine around the weight). Is this part normal? The brine was up to the top; is that too much? I’m assuming the onions are safe to eat, but would appreciate an experienced answer, please!

    • Reply Renee Kohley March 6, 2023 at 9:57 am

      Hi Susan! The white film is not mold! It is called “Kham yeast” and it is perfectly safe, and harmless! Enjoy those onions!

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