Preheat oven to 375°F (190°C) and lightly spray a casserole dish with cooking spray.
In a skillet over medium heat, cook ground turkey until browned. Drain excess liquid if needed.
Stir in cauliflower rice, mushrooms, and bell peppers. Cook for 3–4 minutes until softened.
Mix in marinara sauce, Italian seasoning, garlic powder, onion powder, salt, and pepper.
Pour mixture into prepared baking dish. Top with mozzarella and Parmesan cheese.
Arrange turkey pepperoni slices evenly over the cheese.
Bake for 20–25 minutes until bubbly and cheese is melted.
Let cool for 5 minutes before serving.
