PREPARE and cook Mastering the Meatball recipe. Cool, then cover and refrigerate (or freeze) 24 of the meatballs for another use. Cover remaining 24 meatballs to keep warm.
COOK and stir vegetables in hot oil in large skillet on medium-high heat until tender. Add meatballs and barbecue sauce; mix lightly. Cook until heated through, stirring occasionally.
SPOON 4 of the meatballs into each roll. Top sandwiches evenly with the vegetable mixture and cheese. Place on rack of broiler pan. Broil until cheese is melted.