Onions peel, finely dice. Heat 2 tablespoons of oil in a pot, fry the onions until transparent. Add the tomatoes and juice and chop with a spatula. Season with salt, pepper and 1 pinch of sugar. Bring to the boil and simmer for about 10 minutes.
Drain beans, rinse and drain. Boil the beans in the tomato sauce briefly. Season to taste with salt and pepper. Let cool off. Wash, chop and stir in parsley.