BBQ Cheddar Burgers

In bowl, combine ground beef with onion; mix lightly but well. Shape into four 1/2-inch thick patties. Place patties on grid over medium ash-covered coals. Grill, uncovered, 14-16 minutes or until 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.