Place beef roast and onion into the slow cooker. In a small bowl combine taco seasoning and beef broth. Pour over the beef and onion. Cover and cook on low for 6-8 hours or until tender. Shred the beef using two forks.

Place the beef in a large bowl. Stir in taco sauce and green chilies. Use the shredded beef for whatever you like—quesadillas, tacos, burritos, etc.