Melt the butter into a large skillet over medium-high heat and add the onion, pepper, mushrooms, kale, and a big pinch of sea salt. Cook over medium high heat for about 10 minutes until the veggies are soft, fragrant, and slightly caramelized.
Add the garlic and cook for a minute, and then add the ground beef, Italian seasoning, salt, and pepper. Break the beef up and mix it into the cooked veggies, browning the beef.
Add the marainara sauce and simmer for 5 minutes.