Peel and finely chop the onion. Wash basil, dab dry, chop finely. Mix onion, basil and vinegar, season with salt, pepper and sugar. Beat the oil with a whisk.
Boil the eggs hard for about 9 minutes. Wash, clean and chop the beans. Cook in boiling salted water for about 10 minutes. Clean, wash and cut the peppers into strips. Clean, wash and dry the salad.
Pluck the salad leaves finely. Drain bean water. Rinse beans with cold water and let them cool down. Peel the eggs and cut into slices. Drain olives and artichokes. Cut artichokes into quarters.
Drain the tuna, chop it lightly. Mix all ingredients and marinate with the vinaigrette.