Preheat the oven to 375°F (190°C) and lightly coat a 9x13-inch baking dish with cooking spray or oil.
Place a single layer of frozen cheese ravioli in the bottom of the prepared baking dish, fitting them snugly but without overlapping too much.
Spoon 1 cup of marinara sauce evenly over the ravioli, then sprinkle 1 cup of shredded mozzarella over the sauce.
Repeat with a second layer of ravioli, the remaining 1 cup marinara, and the remaining 1 cup mozzarella. Evenly sprinkle the grated Parmesan over the top.
Bake uncovered in the preheated oven for 20–30 minutes, or until the cheese is melted and bubbling and the casserole is heated through; cover with foil if the top browns too quickly.
Remove from the oven, let rest a few minutes, then sprinkle with fresh parsley if using and serve.