For the beef steaks with oyster mushrooms, wash and coarsely chop mushrooms. Heat oil in a frying pan, sauté onion until translucent, add mushrooms and fry over medium heat until liquid has evaporated.
Season with salt and oregano to taste. Heat oil in a skillet, sear meat on both sides, then reduce heat and fry for an additional 2 minutes on both sides.
Season meat with salt and pepper and wrap in aluminum foil and let rest for 5 minutes. During the resting time, toss the mushrooms in the drippings.
Serve both, and taste.