Lightly shape Ground Beef into four 3/4-inch thick patties. Coat onion with cooking spray. Place patties on grid over medium, ash-covered coals; arrange onion around patties. Grill, covered, 8 to 10 minutes (over medium heat on preheated gas grill, covered, 7 to 9 minutes) until instant-read thermometer inserted horizontally into center registers 160°F, turning occasionally. Season with OFBS Seasoning after turning, as desired. About 1 minute before the patties are done, top each with cheese.

Combine mayonnaise and mustard; spread on top and bottom halves of rolls. Serve burgers and onion in rolls with lettuce and tomato, as desired.