Preheat your oven to 350°F (175°C).
In a large skillet, heat the vegetable oil over medium heat. Add the chopped onion and bell pepper, sautéing for about 5 minutes until they begin to soften.
Add the minced garlic and ground beef to the skillet. Cook until the beef is browned and cooked through, breaking it apart with a spoon, about 7-10 minutes.
Drain excess fat from the skillet if necessary and add the black beans, corn, diced tomatoes, cooked rice, chili powder, cumin, salt, and pepper. Stir until combined, and cook for another 5 minutes to heat through.
Transfer the mixture into a casserole dish. Sprinkle the shredded cheddar cheese evenly on top. If desired, add breadcrumbs for an extra crunchy layer.
Cover the casserole dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and slightly golden.
Once done, remove from the oven and let it sit for a few minutes before serving.