1. In 13x9-inch (3-quart) glass baking dish, place squash, bell peppers and onion. Pour dressing over vegetables. Cover; let stand 1 hour to blend flavors.
2. Heat gas or charcoal grill. Remove vegetables from marinade; reserve marinade. Place squash and bell peppers in grill basket (grill “wok”). Place grill basket on grill over medium heat. Cover grill; cook 5 minutes.
3. Add onion to grill basket. Cover grill; cook 5 to 10 minutes longer, turning and brushing vegetables with marinade 2 or 3 times, until tender. Sprinkle with pepper.

Fresh vegetable grilling chart