1. Gently toss the green beans, onions, potatoes, capers, and parsley. Add the vinaigrette, and let marinate for 2 hours. Drain and reserve the excess vinaigrette.
2. Lay the lettuce on a platter. Place the tuna in the center. Arrange the bean-and-potato mixture around the tuna. Garnish the salad with the tomatoes, eggs, anchovies, and olives. Drizzle with remaining vinaigrette.