Wash the pumpkin, quarter it and scrape out the seeds and fibres with a spoon. Cut the pumpkin with skin into thin slices. Peel and wash the potatoes and cut them into thin slices.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Layer pumpkin and potatoes alternately in an ovenproof dish. Season cream with salt and pepper and pour over the vegetables.
Bake in a hot oven for 40-45 minutes.
In the meantime clean the mushrooms, wash them briefly if necessary and cut them into slices. Peel onion and garlic and chop finely. Heat the oil in a pan in portions. Sauté the mushrooms in it in 2 portions.
Fry the onion and garlic briefly. Season with salt and pepper. Wash parsley and shake dry. Pluck off the leaves and chop finely. Mix approx. 2⁄3 with the mushrooms.
Dice the feta. After about 30 minutes baking time, spread the mushrooms and feta on the casserole. Bake until done. Sprinkle with the rest of the parsley.