In a skillet, cook beef, onion and garlic over medium heat until meat is no longer pink; drain.
Add the tomato sauce, water, tomato paste, salt and oregano; mix well.
Spread 1/4 of the meat sauce in an ungreased 5-quart slow cooker.
Arrange 1/3 of the noodles over sauce, breaking the noodles, if necessary.
Combine the cheeses; spoon 1/3 of the mixture over noodles.
Repeat layers twice, topping with remaining meat sauce.
Cover and cook on low for 4-5 hours or until noodles are tender.