Combine first 8 ingredients. Divide mixture into 6 equal portions, shaping each into a 1/2-inch-thick patty.
Place patties on a grill rack coated with cooking spray; grill 6 minutes on each side or until a thermometer registers 165°. Remove from grill; let stand 5 minutes. Place 1 patty in each pita half; drizzle each serving with 1 tablespoon Easy Tzatziki Sauce.