Heat the oil in a large pan and sauté the onion cubes with the garlic until translucent. Add the frozen spinach and cover and defrost for approx. 10 minutes, stirring occasionally. Season the spinach with salt, pepper and nutmeg. Deglaze with tomato juice and bring to the boil.
Wash tomatoes and cut in half. Add the ravioli and tomato halves to the spinach and heat in the sauce for about 8 minutes. Season the ravioli and spinach pan with salt and pepper and sprinkle with parmesan. Serve with sour cream.