3-4 slices (4 ounces, 115g) hearty, country-style bread (stale)
1 medium red onion, peeled and thinly sliced
1 1/2 tablespoons red wine vinegar, plus extra for soaking the bread and onions
1 teaspoon minced garlic
1 teaspoon sea salt
6 tablespoons best-quality olive oil
3 medium tomatoes (1 3/4 pounds, 800g), diced
1 cucumber peeled, halved, and seeds scraped away, diced
handful fresh basil leaves, about 15 to 20, torn into pieces