Step 1

Preheat oven to 400 degrees F (200 degrees C).

Step 2

Place cauliflower florets in a food processor; pulse into rice-sized pieces.

Step 3

Heat butter and oil in a large skillet over medium heat. Add onion; cook and stir for 2 minutes. Add cauliflower "rice" and mushrooms; cook, stirring frequently, until softened, about 5 minutes. Stir in parsley, garlic, and poultry seasoning. Cook until fragrant, about 1 minute. Remove from heat.

Step 4

Stir chicken, cream of mushroom soup, mozzarella cheese, milk, salt, and pepper into the "rice" mixture.

Step 5

Stand bell peppers cut-side up in a baking dish. Stuff bell peppers with chicken mixture, pushing it down to fill them completely. Sprinkle with cayenne pepper. Cover baking dish with aluminum foil.

Step 6

Bake in the preheated oven until heated through, about 30 minutes. Uncover and continue baking until golden brown, about 15 minutes more.