- 1 cup chopped onion, or more to taste
- 1 (15 ounce) can tomato sauce
- 1/4 cup brown sugar
- 2 tablespoons vinegar
- 4 teaspoons chili powder
- 1 teaspoon soy sauce
- 1 teaspoon salt
- 1/2 teaspoon dry mustard
- 1 1/2 pounds boneless beef chuck roast
- Stir onion, tomato sauce, brown sugar, vinegar, chili powder, soy sauce, salt, and mustard together in a slow cooker; add roast. Spoon onion mixture over the beef to coat.
- Cook on High for 7 hours. Shred meat in slow cooker with a pair of forks. Continue cooking 1 hour more.