Char bell pepper and tomatoes directly over gas flame or in broiler until blackened on all sides. Transfer tomatoes to plate. Enclose pepper in paper bag 10 minutes. Peel, halve, and seed tomatoes; place in blender. Peel, seed, and chop pepper; add to blender. Add oil, vinegar, garlic, and cayenne; blend until smooth. Season sauce with salt and pepper. (Can be made 1 day ahead. Cover and chill.)
