Grill, covered with grill lid, over medium-high heat (350° to 400°) 5 to 6 minutes on each side or until beef is no longer pink.
Cut off 2 inches of bread from 1 side of each pita round, forming a pocket. Line each with 1 lettuce leaf, 2 tomato slices, and 1 red onion slice. Add burger. Drizzle each with 2 tablespoons Tahini Sauce, and sprinkle with 1 tablespoon cheese.