Melt the butter in a large sauce pot over medium high heat and add the onion and pepper with 1 tsp of sea salt. Cook the veggies until soft and sweet, about 7 minutes.
Add the garlic, chili powder, cumin, and cinnamon and stir to combine, cooking for 1 minute.
Add the pumpkin, green chilis, and water, stir to combine and bring to a simmer for 3 minutes.
Turn the heat off and use an immersion blender or regular blender to blend the sauce until smooth. Sea salt and pepper the sauce to your taste.