Heat gas or charcoal grill. In small bowl, mix sauce ingredients; refrigerate until serving time.
In medium bowl, mix all burger ingredients except buns. Shape mixture into 4 patties, about 1/2 inch thick.
Place patties on grill over medium heat. Cover grill; cook 8 to 10 minutes, turning after 5 minutes, until thermometer inserted in center of patties reads 165°F Serve burgers on buns with yogurt sauce.