Place a large skillet over medium heat. Add the ground beef and cook, stirring and breaking up, for 2 minutes. Add the chopped onion and bell pepper and continue cooking until the onion is tender and the beef is browned and no longer pink. Drain well.
To the beef mixture, add the beans. Add salt and pepper, to taste, and blend well. Transfer the mixture to the casserole dish.
Bake in the preheated oven for 20 minutes, until hot and bubbling. Top with the cheese and continue baking for 2 to 3 minutes or until the cheese has melted. Alternatively, sprinkle cheese over each serving.