1. Heat oven to 375 degrees F. Rinse spinach under cool running water. Shake off excess water. Place in large skillet; heat over medium heat 5 minutes or until spinach is wilted.
2. Coarsely chop meatballs and place in large bowl. Add spinach, marinara sauce and 1-1/2 cups of water. Stir to combine.
3. Spoon about 2 cups of the meatball mixture over bottom of shallow 2-1/2-quart casserole. Arrange 1 package of ravioli on top; spread about 2 cups mixture over ravioli and sprinkle with 1 cup cheese. Repeat layering using remaining ravioli, meatball mixture and cheese.
4. Cover with foil. Bake at 375 degrees F for 35 minutes. Uncover; bake 5 minutes or until cheese melts. Let stand 10 minutes; serve.