Tuna Niçoise Salad

Name: Tuna Niçoise Salad
Ingredients: 10 ounces baby yellow or red potatoes (about 2 cups), scrubbed; 1 cup halved crosswise fresh green beans; 3 tablespoons fresh lemon juice; 2 tablespoons finely chopped shallot; 1 teaspoon Dijon mustard; ½ teaspoon salt, divided; ½ teaspoon ground pepper, divided; 5 tablespoons extra-virgin olive oil, divided; 1 tablespoon chopped fresh flat-leaf parsley; 1 (8 ounce) fresh tuna steak; 8 cups torn green leaf or Bibb lettuce; 2 hard-boiled eggs, peeled and halved lengthwise; 1 cup halved cherry tomatoes; ½ cup pitted Niçoise olives