Clean the mushrooms, clean them and unscrew the stalk. Clean, wash and cut spring onions into rings. Heat 1 teaspoon of oil in a pan. Sauté the sauerkraut and spring onions for about 3 minutes.
Stir in the mustard. Season with salt and pepper. Cut turkey breast slices into strips and fold into the sauerkraut. Fill the sauerkraut into the mushrooms and place in an ovenproof dish. Pour on 6 tablespoons of water.
Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes. Heat 1/2 teaspoon of oil in a saucepan. Sauté tomato paste and aiwar in it. Add the stock while stirring and bring to the boil.
Season to taste with salt, pepper and marjoram. Stir in sour cream, do not boil anymore. Arrange stuffed mushrooms with the sauce. Garnish with marjoram.