Barbecue Cheddar Burgers

In a bowl, combine ground beef with onion; Nick slightly but well. Shape into 4 1/2 inch thick patties. Place patties on grid over medium ash covered coals. Grill, uncovered, 14 to 16 minutes or until the centers are no longer pink, turning once. Approximately 1 minute before burgers are done, brush with barbecue sauce; top with cheese. Line bottom half of each roll with lettuce and tomato; top with burger and roll top.