Cut the tomatoes, onions and a mozzarella into small pieces and place in a baking dish. Put the cooked tortellini in the baking dish. Mix the tomatoes with the cream in a bowl and season with salt and pepper. Then mix everything together and distribute it nicely in the mold.
Place the second mozzarella in slices on the casserole and sprinkle with the gratin cheese. Bake the casserole for 30 minutes at 200 ° C (top and bottom heat).