Hold onion rings together by inserting a toothpick through each slice. Grill garlic packet, whole tomatoes and onion rings on uncovered grill over medium coals for about 4 minutes. Carefully turn tomatoes and onion slices, continue grilling 4 min. Transfer tomatoes and onion rings to shallow bowl. Grill bread until browned, 1-2 minutes per side.
Cool, cover and refrigerate half of grilled tomatoes, onion rings and garlic for Grilled Tomato Soup recipe. Peel off and discard skin from remaining tomatoes; remove cores. Remove toothpicks from onion rings. Coarsely chop tomatoes, reserving any juices. Transfer tomatoes and juices to medium bowl.