Cut the bacon into strips and fry them crisply in a pan without fat. Peel and dice the onion and steam briefly. Peel potatoes if necessary and mash them finely with a fork.
Mix lemon juice, 3 tablespoons of water, honey, mustard, pepper and a little salt. Stir in potatoes. Fold in oil, bacon and onion together with frying fat.
Clean the salad, wash thoroughly and spin dry. Clean mushrooms, wash if necessary and slice or cut them into thin slices. Arrange salad and mushrooms on plates and sprinkle with dressing.