In a large bowl, combine the first nine ingredients; set aside 1/4 cup for basting. Pour half into a large bowl. Add chicken; turn to coat. Pour the remaining marinade into another large bowl. Add the zucchini, onions and tomatoes; turn to coat. Cover and refrigerate chicken and vegetables for up to 4 hours or overnight., Drain and discard marinade. Alternately thread chicken and vegetables onto metal or soaked wooden skewers. Grill, covered, over medium heat for 6 minutes on each side or until chicken juices run clear, basting occasionally with reserved marinade.