Peel and halve the onions and cut into thin slices. Sprinkle the onion slices generously with salt, leave to stand for about 10 minutes. Then squeeze out vigorously by hand, wash and drain (this will make them softer and have a more pleasant taste).
Mix the parsley with the onions, add half of the olives, season with salt. Mix everything well. Put the beans in a bowl, cut the tomatoes into small slices and add to the beans. Distribute the onion mixture evenly over the beans.
For the marinade, mix the vinegar with olive oil and season with salt.
Peel and quarter the hard-boiled eggs and place on the salad. Pour the marinade over the salad and let it soak for 30 minutes.
Decorate the salad with the remaining olives and serve cold.