1/3 cup mustard
1/3 cup Worcestershire sauce
3 tablespoons margarine
1 tablespoon prepared horseradish
1 cup chopped onion
1 clove garlic, minced
1 tablespoon light brown sugar
1 tablespoon kosher salt
1 egg
3 pounds boneless, skinless chicken meat - rinsed, dried and chopped
1/2 cup chopped celery
8 hamburger buns
3 (2 pound) onions, sliced into flat rings
2 large tomatoes, seeded and sliced
1/2 cup shredded lettuce
1 1/2 cups shredded Monterey Jack cheese, divided
Mix together the mustard, Worcestershire sauce, margarine, horseradish, onion, garlic, brown sugar and salt - refrigerate well at least 4 hours before serving.
Cover top of buns with strips of lettuce and pieces of celery. Insert slotted spoon into onions for onion rings. Fold in chicken pieces, celery, tomato slices, lettuce, tomatoes and 1/2 cup cheese. Fill buns with beef mixture and cheese mixture. Cover and refrigerate 8 hours before serving.