Place potatoes in a large saucepan; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, until tender, 8-10 minutes, adding green beans during the last 3 minutes of cooking. Drain potatoes and beans; immediately drop into ice water. Drain and pat dry.
In a small bowl, combine salad dressing, lemon zest and pepper. Divide romaine among 4 plates; arrange potatoes, green beans, eggs, tuna and tomatoes over romaine. Serve with dressing mixture.
