Preheat the oven to 375F and grease a 9x13" pan. Place 1/3 cup of the sauce evenly over the bottom of the pan. Then place a layer of the ravioli (no need to thaw or cook them first, they will come out of the oven perfectly tender). After that, spread 1 cup of the chopped spinach, 1/3 of the mozzarella cheese and 1/3 of the parmesan cheese.
Repeat with another layer of ravioli, then 1/3 more sauce and using up all the spinach in this layer. Too it off with 1/3 of each cheese. The 3rd and last layer will just have the ravioli, then sauce and cheeses.
Cover the pan with foil and bake for 35 minutes. Then remove the foil and bake for 15 minutes more, until the cheese is golden and it's all bubbly and completely heated through. Let it sit for 5 minutes before serving. Garnish with some freshly chopped basil or parsley, if you'd like.
