Meanwhile, mix 3 Tbsp. dressing and 1/3 of the garlic. Thread shrimp onto 6 skewers; thread 24 tomatoes onto 6 additional skewers alternately with baguette cubes. Grill all skewers 3 min., turning and brushing occasionally with half the dressing mixture. Remove tomato skewers from barbecue. Place onions, in single layer, next to shrimp skewers on barbecue grate. Grill shrimp and onions 2 to 3 min. or until shrimp turn pink and onions are crisp-tender, turning and brushing occasionally with remaining dressing mixture.