Lightly shape ground beef into four 1/2- inch thick patties.
Place patties in center of grid over medium, ash-covered coals; arrange onion and bell pepper around patties.
Grill patties, uncovered, 11 to 13 minutes to medium (160 degrees F) doneness, until no longer pink in center and juices show no pink color, turning occasionally.
Grill vegetables 13 to 16 minutes or until crisp-tender, turning occasionally. Season with salt and pepper, as desired. Cut bell pepper into 1/2- inch strips.
Spread 1 tbsp cheese on bottom of each bun; top with burger, another 1 tbsp cheese, onion slice and 1/4 of bell pepper. Close sandwiches.
Recipe courtesy of National Cattlemen's Beef Association on behalf of The Beef Checkoff