Preheat oven to 400. Mix meat, cracker crumbs, parmesan cheese and 1/2 cup of the spaghetti sauce in bowl. Shape into 12 meatballs, using about 2 Tbsp. meat mixture for each.
Place, 2 inches apart, in shallow baking pan sprayed with cooking spray. Press 1 cheese cube deeply into center of each meatball.
Bake 14 min. or until meatballs are cooked through. Meanwhile, microwave remaining 1/2 cup spaghetti sauce in microwaveable bowl on HIGH 30 sec. or until heated through.
Apoon sauce evenly into buns. Fill each with 3 meatballs.