Wash green beans, cut into bite-sized pieces and boil in salted water until al dente, strain, refresh and drain well.
Remove the dark green parts of green onions, cut the rest into thin rings.
Wash peppers, cut the flesh into strips and boil in salted water briefly. Refresh and drain well.
Wash and drain lettuce leaves. Drain tuna.
Mix a marinade with vinegar, oil, salt, pepper and parsley. Mix lettuce, onion, peppers and green beans with the marinade.
Pick tuna to pieces and cover the salat with it.