1. Combine first 5 ingredients in a small bowl.
2. Combine onions, parsley, 1/2 teaspoon salt, onion powder, and turkey in a large bowl. Divide mixture into 4 equal portions, shaping each into a 1/2-inch-thick patty.
3. Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add patties to pan, and cook for 4 minutes on each side or until done.
4. Line each pita half with 1 lettuce leaf; add 1 patty, 1 tomato slice, and 2 tablespoons tahini sauce to each pita half.