Chop the onions
Put the salmon in a tin, put a pinch of salt on it.
Clean your mushrooms and chop them (not fine).
Fry mushrooms and onions with butter in a pan. Salt and pepper. Then pour over the grated cheese and stir quickly. (In this particular one I mixed cheese and nuts for a change)
Put the mushroomtoping on top of the salmon.
Shove it in the oven (200 degrees celsius) in 20 minutes. If you want, save some topping and make gravy just by adding some cream.