In a skillet, cook beef and onion over medium heat until meat is no longer pink. Add garlic; cook 1 minute longer. Drain. Stir in the tomato sauce, water, tomato paste, salt and oregano.
Spread a fourth of the meat sauce in an ungreased 5-qt. slow cooker. Arrange a third of the noodles over sauce (break the noodles if necessary). Combine the cheeses; spoon a third of the mixture over noodles. Repeat layers twice. Top with remaining meat sauce.
Cover and cook on low for 4-5 hours or until noodles are tender.