In small bowl, combine feta cheese, 2 tablespoons steak sauce, olives and mayonnaise.
Cover; chill until ready to serve.
Shape beef into 4 patties; grill over medium heat for 5 minutes on each side or until done, brushing with remaining 2 tablespoons steak sauce.
Split open top edge of each pita bread.
Place 1 lettuce leaf in each pita pocket; top each with burger, tomato slice and 2 tablespoons prepared sauce.