1. Crumble ground beef into 2-quart casserole; add onion, celery and green pepper. Cover loosely and microwave on high (100%) 3 minutes; break up and stir. Cover and microwave until very little pink remains in beef, 3 to 4 minutes longer; drain.
2. Stir in remaining ingredients except buns. Cover tightly and microwave on high (100%) until hot, 3 to 5 minutes; stir. Fill buns with beef mixture.