1/2 baguette, cut into 3/4-inch cubes (about 3 cups)
4 tablespoons olive oil
Coarse salt and ground pepper
1 small garlic clove
3 tablespoons fresh lemon juice
2 teaspoons Dijon mustard
1 head Boston lettuce (about 10 ounces), torn into pieces
2 plum tomatoes, cored, halved lengthwise, and sliced 1/2 inch thick
1 English cucumber, halved lengthwise, seeded, and thinly sliced
1/2 cup pitted Kalamata olives, halved
2 cans (6 ounces each) tuna packed in olive oil, drained