Put green beans in a saucepan, bring to the boil and drain.
Peel and dice the onions. Put the beans in a bowl and pour the onion cubes over them.
Bring the stock cube to the boil with 250 ml of water, 4 tablespoons of vinegar and a pinch of sugar in the saucepan. Pour over the warm beans and stir in. Cover and leave to stand in the refrigerator for about 5 hours.
Season the salad with 3 tablespoons of oil and pepper before eating. If you want, you can mix in the bacon cubes.