Cheesy Baked Ravioli

Heat oven to 425 degrees F. Put spinach in a colander in the sink. Mix marinara sauce and sun-dried tomatoes together in a large bowl. In a smaller bowl, combine mozzarella and Parmesan. Bring a large pot of salted water to a boil. Add ravioli and cook just until they float to the surface, 1 to 2 minutes. Drain ravioli over spinach to wilt. Add ravioli and spinach to marinara mixture. Lay down enough ravioli to cover the bottom of a 9- by 1 1/2-inch gratin dish (or bake in individual 4 1/2- to 5-inch gratin dishes). Sprinkle 1/3 of the cheese mixture on top. Repeat with remaining ravioli and cheese mixtures, finishing with the cheese on top. Bake until hot and bubbly throughout, 10 to 12 minutes.