In a small skillet, brown beef and onion in oil; drain. Transfer to a 1-1/2-qt. slow cooker., In a small bowl, combine 1/2 cup water, ketchup, brown sugar, Worcestershire sauce, paprika and mustard; pour over meat. Cover and cook on low until meat is tender, about 5 hours. , Combine flour and remaining water until smooth; stir into meat mixture. Cover and cook until thickened, about 30 minutes longer. , Meanwhile, cook noodles according to package directions; drain. Stir in parsley if desired. Serve with beef.