Preheat the oven to 350°F / 180°C. Tear 180g of stale bread into 1in / 2.5cm pieces. Toss with 1 tablespoon of extra-virgin olive oil and bake for 15 minutes, until crisp outside but soft inside.
Cut 4 medium tomatoes into chunks. Toss with 1 teaspoon of kosher salt in a colander over a bowl. Leave for 10 minutes, keeping the juice.
Whisk 2 tablespoons of red wine vinegar, 1 teaspoon of Dijon mustard, 8 tablespoons of extra-virgin olive oil, 1½ teaspoons of minced garlic, and ¼ teaspoon of salt into the tomato juice.
Chop 1 English cucumber. Toss with the tomatoes, bread, dressing and 1 cup of loosely packed basil leaves. Leave for 5 minutes before serving.
