Spray medium nonmetallic grillproof casserole with nonstick cooking spray; set aside. To make basting mixture, combine 2 tablespoons vinegar with oil in small bowl; set aside.

Prepare Grilled Bell Peppers; set aside. Remove strips of peel from eggplant, lengthwise at 1-inch intervals, and remove ends. Slice eggplant into 1/2-inch-thick rounds. Thread eggplant and onion quarters onto metal skewers; baste. Grill on covered grill over medium coals 20 to 30 minutes or until grill-marked and tender, basting and turning every 10 minutes.

Meanwhile, heat oven to 325°F. Prepare Balsamic-Herb Vinaigrette. Remove eggplant and onion from grill. Cut eggplant into 1/2-inch strips; place eggplant and onion in prepared casserole with Balsamic-Herb Vinaigrette. Cover loosely and place in oven to hold. Or, place casserole on upper rack of grill to hold.

Grill cherry tomatoes. To grill mushrooms, thread whole mushrooms onto 2 or 3 metal skewers; baste mushrooms and cut sides of zucchini. Grill mushrooms and zucchini on covered grill over medium coals 10 to 15 minutes or until browned and tender, basting and turning once. Remove from grill; cut zucchini into 1/2-inch-thick slices. Add zucchini and mushrooms to eggplant mixture.

Dice bell peppers; add bell peppers and tomatoes to eggplant mixture. Stir in remaining 2 tablespoons vinegar and basil. Garnish, if desired.

Grill bell pepper halves, skin side down, on covered grill over medium to hot coals 15 to 25 minutes or until skin is charred, without turning. Remove from grill and place in plastic bag until cool enough to handle, about 10 minutes. Remove skin with paring knife and discard.

Whisk together all ingredients in small bowl; set aside.