Pour the frozen ravioli into a 6-quart slow cooker.
In a medium bowl, stir together the crushed tomatoes, tomato paste, water, onion, minced garlic, Italian seasoning and salt & pepper.
Pour sauce over the frozen ravioli and stir to coat all the ravioli with sauce.
Cover and cook on low for about 5 hours (or high for 3 hours).
There is no need to stir this while it cooks.
About 10 minutes before serving, sprinkle the ravioli with the shredded mozzarella cheese.
Place the cover back on the slow cooker and let the cheese melt.
If you have a smaller family or just don't want leftovers, one bag of ravioli will work. Keep the sauce recipe the same. I used a mix of beef and cheese ravioli. Also, you can substitute sauce ingredients for one large jar of store-bought pasta sauce. Great served with a salad and garlic bread.