Souperburgers

1 pound ground beef
1 medium onion, chopped
1 can cream of celery soup
1 tablespoon prepared mustard
1/8 teaspoon pepper
6 hamburger rolls, split and toasted
In skillet over medium-high heat, cook beef and onion until beef is browned, stirring to separate meat. Pour off fat. Add soup, mustard and pepper. Heat through.
Serve on rolls.