Spray crock pot insert with non stick spray or use a slow cooker liner (much simpler).
Heat oil in large skillet. Brown meat, add onions, and cook until meat is brown and onions are soft. Transfer to crock pot.
Blend tomato sauce, water, brown sugar, vinegar, salt, dry mustard and worcestershire sauce and pour over meat.
Cook on high 6-8 hours or until meat is tender. Serve over noodles or rice.