Chicken fillet with mushrooms Cut the champignons into medium pieces. Chop the chicken fillet coarsely. Chop the onion. Fold a sheet of foil in half, raise the edges. Arrange the chicken, mushrooms and onions, drizzle with olive oil, white wine, season with salt, pepper, nutmeg, add a sprig of thyme. Connect the edges of the foil and send the bundle to the oven for 30 minutes at 180 degrees.