Place garlic and onions, skin sides up, on a jelly roll pan. Place pan on lower oven rack. Broil 30 minutes. Add tomatoes to pan, core sides down. Cook an additional 30 minutes or until blackened. Cool 5 minutes. Remove skins from garlic, onion, and tomatoes; discard skins. Place garlic, onion, and tomatoes in a food processor. Add vinegar and remaining ingredients; process until smooth.