Prepare barley as per package directions, using 1/3 cup barley and 2/3 cup water.
Combine cooked barley and onion in food processor. Whirl until finely chopped. Add beef, barbecue sauce, salt and pepper. Using on-off pulses, mix together just until combined. Shape into 4 patties.
Grill or broil 5 inches from heat for 8 to 10 minutes, turning once. Serve on hamburger buns.