Preheat oven to 350 degrees Fahrenheit.
In a skillet brown ground sausage over medium heat until cooked through, about 8 minutes. Set aside.
Melt butter in same skillet, add diced onion and garlic. Cook for about 5minutes until clear and soft. Add riced cauliflower, season to taste, cook for about 3 more minutes or until just colored. Remove from heat.
In a bowl mix cooked sausage and cauliflower mixture. Add shredded cheese, toss until just combined.
Cut the tops off of bell peppers and remove seeds. Fill each pepper with sausage mixture until full, careful to not over-fill.
Spray an 8x8 baking dish with nonstick cooking spray. Place peppers into dish, bake uncovered for 25 minutes. Top with sliced mozzarella and continue cooking for 5-10 more minutes or until cheese is melted.
Enjoy!