In a medium sized pan on medium heat, add ground beef and cook until meat starts to brown. Drain any fat. Then add in onions, garlic, salt, and pepper.
Add a little over 1/2 cup of meat sauce to bottom of slow cooker and spread around. Follow this with a layer of half of the ravioli.
Next, add a layer of your meat sauce (about half of remaining sauce), then add a layer of cheese (1 cup).
Add remaining ravioli, and layer the remaining sauce on top.
Cover and cook on HIGH for about 2 – 2 1/2 hours, or on LOW for 4-5 hours, or until pasta is tender. Add remaining cheese on top of ravioli, and cover with lid for about 10-15 minutes or until cheese has melted.