Cut the tops off of the peppers, but only discard the stem. Chop up the top piece of the pepper and set aside.
Remove the inside seeds and white parts from the large part of the pepper.
Heat olive oil in a large skillet over medium-low heat. Add the garlic, onion, and chopped up pepper pieces and saute until softened, about 3-4 minutes.
Add the cooked rice, black beans, and corn to the onion mixture. Stir well to combine.
Spoon the bean and rice mixture into the peppers.
Place the stuffed peppers into a baking dish large enough to hold all of the peppers.
Sprinkle about a tablespoon of shredded cheese over each stuffed pepper (optional).
Add enough water to fill the pan ¼ inch up the inside of the dish.
Bake for 25 minutes.
Notes
If you are left with more filling than peppers, the mixture makes a great stuffing for wraps.