Preheat the oven to 350ยบ F. Line a rimmed half sheet pan with non-stick aluminum foil.
Slice the tops off of the sweet bell peppers. Use a spoon to scoop the seeds and white membranes from the insides of the peppers. Discard the pepper tops and seeds. Place the peppers onto the prepared half sheet pan; briefly set aside.
In a large bowl, stir together the diced onion, cherry tomatoes, corn, black beans, and brown rice until combined. Sprinkle the chili powder, oregano, salt, and pepper over top before stirring to distribute the seasonings throughout. Fold 1 cup of the Cheddar cheese into the filling, reserving the remaining cheese for later.
Stuff the open cavities of the sweet bell peppers tightly with filling, mounding a bit of the filling over the top edge of the peppers. Sprinkle the remaining Cheddar cheese over top of the filling. Bake the stuffed peppers for 30 to 35 minutes or until filling is heated through, the peppers soften, and the exteriors begin to wrinkle. Serve immediately.