In small bowl, mix 1/2 cup of the yogurt and remaining sauce ingredients; refrigerate until serving.
Heat gas or charcoal grill. In medium bowl, mix all burger ingredients and remaining yogurt. Shape mixture into 4 patties, about 1/2 inch thick.
Place patties on grill over medium heat. Cover grill; cook 8 to10 minutes, turning after 5 minutes, until meat thermometer inserted in center of patties reads 160°F. Place burgers on buns; top with tomato slices and sauce.