Wash the beans and soak them in cold water overnight. Boil the beans with the soaking water and 1 teaspoon of salt. Cover and cook on low heat for 1 1/2 hours. In the meantime, clean and wash the salad and cut into fine strips.
Drain the corn. Peel and quarter onion and cut into thin slices. Put the beans on a sieve and rinse under cold running water. Mix beans, salad, corn and onion and arrange on a plate