Combine the ground beef mixture, rice, tomatoes, black pepper, and salt in a large bowl and mix until blended.
In a 9x13x2-inch baking dish, place the bell peppers cut-side up. Evenly divide the beef mixture among the pepper halves. Cover the dish with foil and bake for 20 minutes. Remove the foil and sprinkle the cheddar on top.
Return the pan to the oven, uncovered, and bake until the cheese melts, about 5 minutes.