Preheat oven to 375 degrees. Slice each bell pepper in half to create two pepper boats for stuffing, and remove the inner seeds and stem.
Place the hollowed out peppers on a baking sheet and lightly season with salt and pepper.
In a large pan, remove sausage from casing and start to brown it over medium heat.
Dice half a yellow onion and add it to the pan while the sausage is cooking.
Once the sausage is nearly cooked, add the riced cauliflower, finely minced mushrooms, and diced spinach to the pan. Continue to cook until the cauliflower has softened, and the spinach is fully wilted.
Stir in the tomato paste, oregano, garlic and onion powder; cook an additional 2 minutes to combine the flavors.
Take the pan off the heat, and stir in the parmesan cheese before dividing the sausage mixture into each of the 6 red pepper halves.
Top each filled pepper with a sprinkle of mozzarella cheese, and place the baking sheet in the oven.
Cook the peppers for 25-30 minutes, until peppers are tender and the cheese is fully melted. Turn the broiler on for the last minute or two of cooking to give the cheese and pepper edges a crisp. Serve hot with red pepper flakes and additional parmesan cheese.
Recipe by DomestikatedLife at https://domestikatedlife.com/2018/01/24/sausage-and-cauliflower-stuffed-peppers/