Wash the potatoes and cook in boiling water for 20 minutes. Clean, wash and halve the beans. Cook in boiling salted water for 15 minutes. Boil eggs hard for 10 minutes. Clean, wash and slice the tomatoes.
Mix vinegar, two tablespoons of water, salt, pepper and sugar. Whip the oil into the mixture. Peel onions. Wash the parsley. Chop both and stir into the marinade. Drain the potatoes, peel them, let them cool down a little and cut them into slices.
Peel the eggs and cut into eighths. Drain beans. Clean, wash and drain the salad. Drain tuna. Carefully mix potatoes, eggs, tomatoes, beans, tuna and olives with the marinade.
Season again. Line a plate with the salad leaves and arrange the salad on top. Baguette tastes good with it.