MIX dressing and basil until blended; pour over fish in shallow dish. Stir to evenly coat. Refrigerate 15 min. to marinate.
HEAT grill to medium-high heat. Remove fish from marinade; discard marinade. Thread fish onto 4 skewers alternately with onions and zucchini.
GRILL 4 to 5 min. on each side or until fish flakes easily with fork and vegetables are crisp-tender.