Preheat oven to 350 degrees.
Lightly spray baking dish with nonstick cooking spray.Spoon a small amount of marinara sauce into the bottom of a baking dish or dutch oven. Add a single layer of ravioli (about 1/3 of the bag).
Sprinkle with a handful of cheese.
Add a handful of spinach.
Pour half of the remaining sauce on top and spread with a spoon.
Add another layer of ravioli (1/3 of the bag).
Add a second layer of cheese.
Add a second handful of spinach.
Add remaining sauce over spinach and spread with a spoon.
Add remaining ravioli and sprinkle with mozzarella cheese.
Sprinkle with parmesan cheese.
Cover with foil or a lid and bake for 30 minutes.
Uncover and bake an additional 15-20 minutes. Ravioli bake should be bubbly.
If you'd like to brown the cheese on top you can turn on the broiler for a minute or two (watch carefully to prevent burning). Serve with garlic bread and salad!