1. Soak wood chips in water 30 minutes; drain.
2. Remove grill rack; set aside. Preheat grill to high heat. Place wood chips on hot coals; heat wood chips 10 minutes. Coat grill rack with cooking spray; place grill rack on grill.
3. Finely chop green onion tops; set aside. Thread white parts of green onions onto a skewer. Thread red onion quarters onto skewers. Thread garlic cloves onto a skewer. Lightly brush vegetables with oil.
4. Place green onion, red onion, and garlic skewers on the grill; grill 1 minute on each side or until darkly browned on the outside but still raw in the center. Remove from grill; cool. Place bread on grill; grill 1 minute on each side or until darkly toasted. Remove from grill. Place tomatoes and bell peppers on grill; grill tomatoes 2 minutes on each side or until skins are charred. Grill peppers 3 minutes on each side or until charred. Remove from grill; cool. Scrape and discard charred skins from 3 tomatoes and both peppers with a paring knife. Remove and discard seeds and membranes from peppers.
5. Combine grilled vegetables, bread, remaining oil, cucumber, and remaining ingredients in a blender or food processor; process until smooth. Chill 1 hour. Ladle 3/4 cup gazpacho into each of 8 bowls; sprinkle with green onion tops.