Assemble Burritos - Warm tortillas in microwave oven for 30 seconds, either in original packaging or wrapped in moist paper towels. One-by-one, place a tortilla on a slightly larger foil surface, place a ¼-inch strip of warmed rice just below the center, and then top rice with beef, corn, beans, tomato, lettuce, and a pinch of red onion. Roll the bottom over the filling by an inch, wrap shorter side over the filling and then roll the whole thing up to a large tight cylinder with 1 end open. Wrap in the foil or melt cheese over them and serve.