Preheat oven to 350.
Add olive oil to a large pan set to medium heat.
Brown Italian sausage for 3-4 minutes.
Add onions, mushrooms, riced cauliflower, salt, pepper, and Italian seasoning until vegetables are mostly tender, about 5 minutes.
Add tomato paste and broth.
Stir well to combined.
Simmer filling for 8-10 minutes under low-medium heat.
Stir in parmesan cheese.
Adjust seasoning if needed.Slice peppers in half (lengthwise) and scoop in filling.
Top with mozzarella cheese and bake for 20-25 minutes until tops are golden brown.
Garnish with fresh basil.