Heat the olive oil in a large ovenproof skillet or Dutch oven over medium-high heat. Add the ground beef and diced onion, then cook for 5–7 minutes while breaking the meat into small pieces, until the beef is browned and the onion is softened; drain excess fat if needed.

Stir in the minced garlic and diced bell peppers. Cook for 2–3 minutes, just until the garlic is fragrant and the peppers begin to soften while still retaining some color.

Add the undrained diced tomatoes, tomato sauce, beef broth, uncooked rice, Italian seasoning, Worcestershire sauce, kosher salt, and black pepper. Stir thoroughly so the rice is distributed through the liquid and the seasonings coat the beef and vegetables.

Bring the mixture to a boil, then reduce the heat to low. Cover the skillet tightly and simmer for 18–22 minutes, stirring once or twice to keep the rice from sticking and to help it cook evenly.

Remove the lid and check the rice for tenderness. Most of the liquid should be absorbed; if the rice needs a little more time, replace the lid and continue cooking briefly until tender.

Sprinkle the shredded cheddar or Monterey Jack evenly over the casserole. Cover for 1–2 minutes until the cheese melts, or place the ovenproof skillet under a broiler briefly until the cheese is bubbly.

Let the casserole rest for 5 minutes before serving. This short rest allows the rice to absorb remaining liquid and helps the casserole firm up for neat, generous portions.