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 12 minutes or until blackened and charred. Place in a zip-top plastic bag, and seal. Let stand 15 minutes. Peel and discard skins.
Place zucchini on a foil-lined baking sheet, and coat with cooking spray. Broil for 5 minutes or until tender and lightly browned. Cool.
Dice roasted peppers and zucchini; combine with basil and remaining ingredients except bread, tossing to coat. Let stand 30 minutes. Spoon 2 tablespoons relish over each bread slice.