Wash and clean the green beans and cook them in boiling salted water for about 12 minutes until al dente. Drain, rinse with cold water and let cool off.
Rinse and drain the white beans. Drain tuna and pluck roughly. Peel onions and cut them into thin strips.
Mix vinegar, mustard, salt, pepper and sugar. Fold in the oil well. Mix the prepared salad ingredients, olives and capers with the salad dressing and leave to stand for approx. 20 minutes. Goes well with baguette or grilled food.