Preheat the oven to 175° C/350° F in fan mode.
Place a pot full of water over high heat. Once the water is well boiled, salt and add the ravioli boiling 2 minutes less than the time indicated on the package, so that they come out al dente.
Spread some tomato sauce in a 28x17cm (11x 7 inches) casserole, place half of the ravioli on top and season with salt and pepper.
Cover the ravioli with half the spinach, drizzle with a little tomato sauce and sprinkle with half the mozzarella.
Drizzle with a little more tomato sauce, place the remaining ravioli on top, season with salt and pepper and cover with the remaining spinach.
Drizzle with the rest of the tomato sauce and sprinkle with the rest of the mozzarella.
Bake for 30-35 minutes, remove from oven, let the ravioli cool for 5 minutes and serve.