Preheat the Oven: Begin by preheating your oven to 375°F (190°C). Lightly grease a 9×13-inch casserole dish to prevent sticking. This temperature creates the perfect environment for cooking the rice evenly while developing flavors throughout the dish.

Cook the Ground Beef: Heat a large skillet over medium-high heat. Add the ground beef and cook until thoroughly browned, about 5-7 minutes, breaking it into crumbles as it cooks. If your beef is lean, you may add the optional tablespoon of olive oil to prevent sticking. Once the beef is browned, add the diced onion, bell pepper (if using), and minced garlic. Cook for another 3–4 minutes until the vegetables have softened. Season the mixture with smoked paprika, oregano, salt, and black pepper, stirring well to distribute the spices evenly.

Combine Casserole Ingredients: Add the uncooked rice directly to the beef mixture in the skillet, stirring to coat the grains with the flavorful meat juices. Pour in the beef broth and canned tomatoes with their juice, which will provide the necessary liquid for cooking the rice. If using frozen vegetables, add them at this point. Bring the entire mixture to a gentle boil, allowing the flavors to begin melding together.

Assemble the Casserole: Carefully transfer the beef and rice mixture to your prepared casserole dish, spreading it out evenly. Cover the dish tightly with aluminum foil to create a sealed environment that will trap steam and ensure the rice cooks properly without drying out. Place in the preheated oven and bake for 30–35 minutes, or until the rice is tender and has absorbed most of the liquid.

Add the Cheddar Crust: While the casserole is baking, prepare the topping by combining the shredded cheddar cheese, panko breadcrumbs, and melted butter in a small bowl. Mix until the ingredients are well incorporated. Once the casserole has finished its initial baking time, remove it from the oven and take off the foil. Sprinkle the cheese mixture evenly over the top of the casserole, creating a complete layer.

Bake and Serve: Return the uncovered casserole to the oven and bake for an additional 10–12 minutes, until the cheese is completely melted and bubbly, and the breadcrumb topping has turned a beautiful golden brown. Remove from the oven and allow the casserole to rest for 5 minutes before serving. This resting period allows the flavors to settle and makes portioning easier.