Preheat oven to 350 degrees. Cook ravioli according to package directions and drain. Meanwhile in a large skillet, brown ground beef and then drain. Stir in spaghetti sauce and spinach. Spoon and spread half of beef mixture into an 8 inch square baking dish. Arrange ravioli over beef layer. Spoon and spread remaining beef mixture over ravioli. Cover with foil and bake for 20 minutes. Uncover and sprinkle with cheese. Bake an additional 5 to 10 minutes or until casserole is bubbly and cheese is melted.