1. Preheat your oven to 375°F (190°C).
2. In a large oven-safe skillet, heat the olive oil over medium heat. Add the ground beef and cook until browned, breaking it apart with a wooden spoon, about 5 minutes.
3. Add the chopped onion and minced garlic to the skillet. Sauté until the onion becomes translucent, around 3 minutes.
4. Stir in the chopped bell peppers and cook until they begin to soften, about 4 minutes.
5. Add the uncooked rice, beef broth, diced tomatoes, tomato paste, oregano, basil, salt, and pepper. Stir to combine, ensuring the rice is submerged in the liquid.
6. Bring the mixture to a boil, then reduce the heat to low. Cover the skillet and let it simmer for 18-20 minutes, or until the rice is cooked and has absorbed most of the liquid.
7. Once cooked, remove the skillet from heat and sprinkle the mozzarella cheese evenly over the top.
8. Transfer the skillet to the preheated oven and bake for 10 minutes, or until the cheese is melted and bubbly.
9. Remove from oven and let the casserole sit for a few minutes before serving. Garnish with fresh parsley if desired.

Pro tip: If you don’t have an oven-safe skillet, simply transfer the mixture to a baking dish before adding the cheese and baking it.