Heat greased grill to medium heat.
Prepare Dinner as directed on package. Meanwhile, mix meat and 3 Tbsp. barbecue sauce. Shape into 6 (1/2-inch-thick) patties.
Grill patties 7 to 9 min. on each side or until done (165°F), brushing occasionally with remaining barbecue sauce. Top with Singles; grill 1 min. or until melted.
Fill buns with burgers, lettuce and tomatoes. Serve with macaroni & cheese and watermelon.