Combine first 6 ingredients in a large bowl. Divide turkey mixture into 4 equal portions, shaping each into a 3/4-inch-thick patty. Place patties on grill rack coated with cooking spray; grill 6 minutes on each side or until done.
Spread 2 tablespoons Special Sauce over top half of each bun. Place lettuce leaves on bottom halves of buns; top each with 1 patty and top half of bun. Cut each burger in half.
To make Special Sauce:
Combine all ingredients in a medium bowl. Cover; refrigerate.