Wash and drain the spinach. Peel and chop onion and garlic. Heat 1 tablespoon of oil in a large frying pan. Sauté the garlic briefly in it. Add the spinach dripping wet and let it collapse. Season to taste with salt, pepper and nutmeg.
Heat 1 tablespoon of oil in a large pot. Sauté the onion until transparent. Deglaze with pizza tomatoes and approx. 1⁄8 l water. Stir in stock and simmer covered for about 2 minutes.
Wash and chop the basil. Dice half the mozzarella, cut the rest into slices. Add ravioli, spinach, basil and mozzarella cubes to the sauce. Pour everything into a greased casserole dish and cover with mozzarella slices. Gratinate in a preheated oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer) for approx. 10 minutes.