Pour the beans into a sieve, rinse and drain. Peel and finely chop the onions. Cut ham into thin strips. Mix everything.
Mix vinegar with 2 tablespoons of water, salt, pepper and sugar. Beat the oil down in a thin stream. Mix vinaigrette and salad. Season to taste again. Wash the chives, shake dry, cut into small rolls and sprinkle over the salad.