Step 1

Preheat oven to 375°F. Toss together bread, ¼ cup of the oil, ½ teaspoon of the salt, and ¼ teaspoon of the pepper on a large rimmed baking sheet; spread mixture in an even layer. Bake until golden brown and crispy, about 15 minutes, tossing once halfway through cook time.

Step 2

Toss together tomatoes, cucumber, arugula, basil, tarragon, capers, and toasted bread in a large bowl; set aside.

Step 3

Stir together vinegar, mustard, garlic, and remaining ⅓ cup oil, 1 ½ teaspoons salt, and ¼ teaspoon pepper in a small bowl until combined. Drizzle over tomato mixture in bowl; gently toss to combine. Let stand at room temperature 30 minutes. Serve.