Place plastic colander in a 2-quart microwave-safe casserole. Combine onion, green pepper, and crumbled ground beef in colander. Microwave (high or 100% power) for 6 minutes, stirring once halfway through cooking. Remove colander and pour off drippings. Turn meat mixture into casserole. Add tomato sauce, tomatos, beans, salt, chili powder, black pepper, and mustard. Cover. Microwave (high or 100% power) for 10-12 minutes, stirring halfway through cooking. Rest, covered, for 5 minutes.