Tomato, Basil, and Cucumber Summer Panzanella

Ingredients

• 1 (1-pound) day-old rustic or sourdough bread loaf
• 1/3 cup olive oil
• 1/4 teaspoon kosher salt, or to taste
• 1/4 cup finely chopped shallots
• 1/4 cup red wine vinegar
• 2 tablespoons aged balsamic vinegar (such as Monari Federzoni)
• 4 very ripe small tomatoes (about 1 pound)
• 8 fresh basil leaves, torn into large pieces
• 1/2 cup extra-virgin olive oil
• 2 garlic cloves, smashed
• 1/2 teaspoon plus a pinch of kosher salt
• 3/4 cup thinly sliced red onion
• 1 tablespoon red wine vinegar
• 1 pint cherry tomatoes
• 1 1/2 pounds Early Girl or other flavorful ripe tomatoes, cored and cut into bite-size pieces (about 3 1/2 cups)
• 1 1/4 teaspoons kosher salt, or to taste, divided
• 4 Persian cucumbers (Or any cucumber), peeled and cut into 1/2-inch-thick slices (about 2 1/4 cups)
• 16 fresh basil leaves, torn into large pieces
• Flaky sea salt (such as Maldon)