- In a bowl, whisk together all of the ingredients. Season with salt and pepper. Set aside.
- Place the potatoes in a pot. Cover with cold water and season with salt. Bring to a boil and simmer for 12 minutes or until just tender. Drain and let cool on a large plate.
- Meanwhile, in a pot of salted boiling water, cook the green beans for 2 minutes. With a slotted spoon, remove the green beans and plunge into ice water. Place a steaming basket in the pot. Place the eggs in the basket. Cover and cook for 9 minutes. Plunge the eggs in the ice water to immediately stop the cooking. Drain. Peel the eggs. Set the eggs and green beans aside.
- In a small bowl, combine the water, vinegar and sliced onion. Let marinate for 2 minutes. Drain.
- In shallow dishes, arrange the lettuce, bell peppers, cucumber, tomatoes, potatoes, green beans and onion. Top with the eggs cut in half, tuna and olives. Drizzle with the dressing.
Baby potatoes can be used instead of fingerling potatoes.