Clean the beans, break them into pieces and wash them. Cook the beans in boiling salted water for 15 minutes. Cut bacon into small cubes. Peel and finely chop the onion. Heat oil in a pan and fry bacon.
Add the onion and fry briefly. Deglaze with vinegar and 3 tablespoons of water. Stir in marjoram and mustard. Season to taste with salt, pepper and sugar. Drain the beans and add the marinade.
Let everything go through. Wash and drain the lettuce leaves. Spread the lettuce leaves on the plates. Arrange bean salad on top. Garnish with halved cherry tomatoes and marjoram. Fried slices of bread taste good with it.