Preheat the oven to 375 degrees F. Spray a baking dish with cooking spray.
In a large skillet over medium heat, cook the ground beef until browned. I also seasoned the ground beef with garlic powder, onion powder, salt, and pepper. Drain any excess grease. Add the onion and garlic, cook 2-3 minutes until softened.
Stir in the riced cauliflower, Italian seasoning, salt, pepper, and 3/4 cup of marinara sauce. Simmer 3-4 minutes to blend flavors.
Place the hollowed peppers in the baking dish. Spoon the filling into each one, packing lightly.
Spoon the remaining marinara over each pepper, sprinkle with Parmesan and mozzarella cheese.