Crisp croutons add a toasty crunch to this twist on tuna salad. Make them in a skillet instead of the oven to keep the kitchen heat down.
In a large skillet, toss bread with 2 tablespoons oil; season with salt and pepper. Cook over medium heat, tossing frequently, until croutons are golden and crisp, 10 to 12 minutes. Set aside.
Finely chop garlic, and sprinkle with salt. Using a chef's knife, press the flat side of the blade back and forth across garlic to make a paste. Transfer to a large bowl; whisk in lemon juice, mustard, and remaining oil. Season dressing with salt and pepper.
To bowl, add lettuce, tomatoes, cucumber, olives, and croutons; toss to combine. Divide salad among four plates, and top with tuna.
Tuna packed in olive oil is firmer and tastier than the water-packed variety. Crushing the garlic into a paste helps create a smooth, well-balanced dressing.