In a large skillet, cook the ground beef over medium heat until browned. Drain any excess fat.
In a mixing bowl, combine the cooked beef, marinara sauce, chopped bell peppers, sliced black olives, dried oregano, garlic powder, salt, and black pepper.
Transfer the mixture to a baking dish and spread it out evenly.
Sprinkle the shredded mozzarella cheese on top.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes before serving.
Notes:
This gluten-free pizza casserole is a hit with kids and adults alike. Feel free to add your favorite pizza toppings!