Dice the onions or cut into rings, whichever you prefer. Wash or brush the mushrooms. Brushing is better because then no flavor is lost.
Then sauté the onions in a good amount of oil and add the mushrooms. Let the whole thing stew and add the spices. First a pinch and then season to taste. The mushrooms should be well seasoned, I found out that the fondor can do a lot.
Then just add the salad sauce. If you like, you can refine it with paprika powder or something similar.