Clean, wash and possibly chop the spinach. Peel and chop onion and garlic. Fry them in hot oil until translucent. Add the spinach and let it fall together. Season with salt, pepper and nutmeg.
Put the spinach aside. Bring the stock to the boil, sprinkle in lentils and cook for about 10 minutes. Wash parsley, dab dry and chop. Stir into the lentils. Clean the mushrooms, unscrew the stems.
Remove the rind from the cheese, dice it and mix it with the spinach. Add to the mushroom heads. Put the mushrooms in a baking dish. Add lentils. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 15 minutes.
Garnish as desired with fresh oregano.