In a medium skillet, crumble and brown the ground beef over medium heat until completely browned. Drain off the excess fat
Reserve ¾ cup of the spaghetti sauce; set aside. Add the remaining spaghetti sauce to the skillet with the ground beef. Stir well then cover and simmer over medium-low heat for 10 minutes, stirring occasionally.
Spread ¼ cup of the reserved spaghetti sauce into the bottom of a 9x13 inch glass baking dish. Arrange one third of the frozen ravioli in a single layer in the pan.
Top the ravioli in the pan with half of the ground beef mixture, then sprinkle with ⅓ cup of the shredded mozzarella cheese.
Place another ⅓ of the frozen ravioli in a single layer over the meat sauce and cheese. Top with the rest of the meat sauce and another ⅓ cup of the shredded mozzarella cheese.
Place the final ⅓ of the frozen ravioli on top of the casserole. Top with the remaining ½ cup of the spaghetti sauce. Sprinkle with the remaining ⅔ cup of shredded mozzarella cheese
Bake the casserole at 350F for 30-40 minutes, until the cheese is completely melted and beginning to bubble around the edges.
NOTE: some readers have mentioned that they liked it better with extra sauce and in a smaller dish so it created deeper layers. Give that a try!