Cut bell peppers in half lengthwise; discard seeds and membranes. Place pepper halves, skin sides up, on a foil-lined baking sheet; flatten with hand. Broil 15 minutes or until blackened. Place in a zip-top plastic bag; seal. Let stand 15 minutes. Peel and finely chop.
Combine bell pepper, onion, basil, and cilantro in a medium bowl. Combine vinegar, oil, sugar, and black pepper in a small bowl, stirring with a whisk. Pour vinegar mixture over bell pepper mixture, tossing to coat. Cover and chill 2 hours. Serve with bread slices.