Add beef and onion to Colander and place on 1¾-Qt./1.75 L Casserole. Cover and microwave on high power 5–6 minutes, stirring halfway through. Drain and wipe Casserole clean. Transfer meat to 1¾-Qt./1.75 L Casserole, add tomatoes, enchilada sauce and rice. Stir to combine. Place peppers, cut side down, on top of meat mixture. Stack and cook. At the end of cooking time, spoon mixture over each pepper and top with cheese.