Preheat your oven to 375°F (190°C).

Cut the tops off the bell peppers and remove the seeds.

In a mixing bowl, combine the cooked rice, black beans, corn, diced tomatoes, cumin, and chili powder.

Fill each bell pepper with the rice mixture and top with cheese if desired.

Place the stuffed peppers in a baking dish and cover with aluminum foil.

Bake for 30 minutes, then remove the foil and bake for an additional 10 minutes until the peppers are tender.

Let cool slightly before serving.