1. On metal or soaked bamboo skewers, alternate meatballs, zucchini, summer squash, tomatoes and onions.
2. Grill, uncovered, over medium heat for 6 minutes, turning once.
3. Baste with barbecue sauce.
4. Grill 8-10 minutes longer or until meatballs are heated through and vegetables are tender, turning and basting frequently.
5. Serve over rice.