Set oven to Broil. Cut cheese into 4 1-ounce slices, and slice tomato.
In a small bowl, mix together mustard and mayonnaise.
Place bottom halves of the bagels on an ungreased cookie sheet, and spread the mayo mixture over each.
Top each with turkey and cheese.
Broil 4-6 inches from heat for 2-3 minutes or until cheese is melted, then remove from heat and top with tomato, lettuce, and the remaining bagel halves.