Preheat the oven to 375 degrees. Coat a 9x13 baking dish with a light coating of cooking spray or oil.
Place a single layer of ravioli on the bottom of the baking dish.
Spread 1 cup of the marinara over the noodles and top with 1 cup of the mozzarella cheese.
Repeat the layer of noodles, marinara and mozzarella again. Sprinkle the top with parmesan.
Bake in the preheated oven for 20-30 minutes or until the cheese is melted and the casserole is cooked through. If the top is getting dark, you can top with aluminum foil.
Sprinkle with fresh parsley before serving.
I used two 12 ounce packages of frozen cheese ravioli. Packages come in different sizes, you'll need about 24 - 30 ounces of ravioli total.
You can use fresh ravioli but it will cook much faster. (I haven't tested this method but it will work) Start checking the casserole when the cheese starts to bubble, likely after 10-15 minutes. You want to pull the ravioli out before it overcooks and becomes gummy, but it should be hot all the way through.
A generous sprinkle of dried oregano and parsley over the top of the cheese is also delicious.