Combine first 12 ingredients in a large bowl; stir until just combined. Divide mixture into 8 equal portions; shape each portion into a (2-inch) patty. Place patties on a jelly-roll pan coated with cooking spray. Broil 4 minutes on each side or until desired degree of doneness. Place 1 tomato slice and 1 patty in each pita half; top each half with 1 1/2 teaspoons yogurt.