Clean the spinach, wash it several times thoroughly and let it drip off easily. Peel onion and garlic. Chop the onion finely, chop the garlic. Heat the oil in a pot and sauté the onion and garlic. Add the spinach, cover and let it collapse and stew for about 5 minutes. Stir in between. Season spinach with salt, pepper and nutmeg
Whisk together the milk, egg, a little salt, pepper and nutmeg. Wash the fish, dab dry and cut in half. Sprinkle fish with lemon juice and salt lightly. Divide the spinach into 2 ovenproof dishes and place 1 fish fillet on each. Pour egg milk over the fish and sprinkle with parmesan. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 20 minutes