Shed the trout, wash and pat dry. Season with salt and pepper completely (including the abdominal cavity) and place thick parsley in the abdominal cavity. Cut the butter into 4 flat pieces and place in the abdomen. Put the fish in the foil. Clean the vegetables and cut into small cubes (very important, otherwise the fish is ready, but the vegetables are not!), Except for the mushrooms, which are cut into slices as normal.
Place the vegetables in the aluminum foil with the fish, close the aluminum foil and roast in the oven at 200 ° for approx. 40 minutes.
You can also take other fish of the same size (e.g. perch). But the great thing is that the vegetables are not compulsory, as you can just take whatever is in the garden or whatever you want.