For glaze, stir together mustard and preserves; set aside. In a medium bowl combine egg, rolled oats, celery, dried cherries (if desired), salt, and pepper. Add ground turkey; mix well. Shape turkey mixture into four 3/4-inch-thick patties.
For a charcoal grill, grill patties on the rack of an uncovered grill directly over medium coals for 14 to 18 minutes or until no longer pink (165 degrees F), turning once halfway through grilling and brushing with glaze during the last minute of grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place burgers on grill rack over heat. Cover and grill as above.)
Serve burgers on buns. Brush any remaining glaze over burgers. If desired, serve burgers with mayonnaise, lettuce, and tomato. Makes 4 burgers.