Preheat the oven to 375°F and lightly grease a 9x13-inch baking dish with cooking spray or a little oil.
Arrange a single layer of frozen cheese ravioli in the bottom of the prepared baking dish.
Spoon 1 cup of marinara sauce over the ravioli, spreading it to cover the pasta, then sprinkle 1 cup of shredded mozzarella evenly on top.
Repeat with a second layer of ravioli, the remaining 1 cup marinara, and the remaining 1 cup mozzarella.
Sprinkle the grated Parmesan evenly over the top layer of mozzarella.
Bake in the preheated oven for 20–30 minutes, until the cheese is melted and the casserole is heated through; tent with foil if the top browns too quickly.
Remove from the oven and sprinkle with fresh parsley, if using, then let rest briefly before serving.