Wash off beef roast and cut into a few pieces. Chop onion and lay on bottom of slow cooker. Place beef on top of onions. Mix the sauce, seasoning, salt and pepper and pour over top the meat.
Cook on low setting for a minimum of 5-6 hours then take out of slow cooker, shred the beef, return to the slow cooker with the sauce and heat through.
Serve over safe noodles or a grain like rice, or it can be spooned into a roll or bun and made into shredded beef sandwiches.