Preheat the oven to 200 °. Drizzle the saithe with the lemon juice. Peel and finely chop the onion / s. Clean and chop the mushrooms. Sauté the onion cubes in the butter for 1 minute, add the mushrooms, season with salt, pepper and sauté again, then add the parsley. Salt and pepper the fish fillets, place in an ovenproof dish and add the white wine. Brush the fillets with the mushroom mixture. Cook covered in the oven for 40 minutes. With a green salad.