In a small bowl, combine the onion, garlic and seasonings; crumble beef over mixture and mix well. Shape into six patties. , Grill, covered, over medium heat or broil 4 in. from the heat for 5-7 minutes on each side or until a thermometer reads 160degrees and juices run clear. , Meanwhile, in a small bowl, combine the lettuce, cucumber, yogurt and sesame seeds. Top each burger with lettuce mixture; serve with pita breads.