Tomato and Bread Salad

Name: Tomato and Bread Salad
Ingredients: 1/2 loaf (11 oz./300 g) country levain, sourdough or any other crusty bread; 1/2 cup (4 fl. oz./120 ml) extra-virgin olive oil; 1/2 cup (4 1/4 oz./135 g) Dijon mustard; Kosher salt and freshly ground pepper; 1 lb. 11 oz. (760 g) large heirloom tomatoes (3 to 4), cut into 1- to 2-inch (2.5- to 5-cm) chunks; 1/2 medium red onion, thinly sliced on the grain (from root to stem); 1 large yellow bell pepper, cut into 1- to 2-inch (2.5- to 5-cm) chunks; 2 to 3 Persian (mini) cucumbers, cut into 1/2-inch (13-mm) coins; Coarse sea salt; 1/4 cup (2 fl. oz./60 ml) red or white wine vinegar; 1 garlic clove, grated on a Microplane or finely chopped