Clean the mushrooms and cut them into leaves. Finely dice the onion and sauté together with the mushrooms in the butter. Chop the pepper (or, if not available, a red pepper) very small, removing the seeds. Add to the mushrooms together with the soy sauce, sherry and very finely chopped ginger. Cook the whole thing for another 5 minutes until the liquid has evaporated. Serve sprinkled with parsley.
Grainy rice or just a piece of white bread goes well with it.