Heat a large skillet over medium-high heat. Add the ground beef and cook, breaking it up with a wooden spoon, until it's no longer pink, about 5-7 minutes.
Add the diced onion and minced garlic to the skillet. Cook for another 2-3 minutes until the onion is translucent and fragrant.
Stir in the diced bell pepper and cook for an additional 2 minutes.
Add the rice, beef broth, diced tomatoes (with their juice), oregano, cumin, salt, and pepper. Stir to combine all ingredients.
Bring the mixture to a boil, then reduce the heat to low. Cover the skillet and let it simmer for about 18-20 minutes, or until the rice is tender and has absorbed most of the liquid.
Stir in the frozen corn and continue cooking for another 2-3 minutes until the corn is heated through.
Sprinkle the shredded cheese over the top of the casserole. Cover the skillet again and let it sit for a few minutes until the cheese is melted.
Garnish with fresh cilantro if desired, and serve hot.