Split a piece (about 3 1/2 by 5 in.) of ciabatta bread (or a crusty roll) in half lengthwise. Toast lightly. Spread cut sides generously with mayonnaise. Cover bottom half with 4 to 6 large fresh basil leaves and a thick layer of 4 to 6 slices firm-ripe large tomatoes. Sprinkle with salt and fresh-ground pepper to taste. Top with 2 slices crisp-cooked bacon. Cap with top half of ciabatta (or top half of roll).