3 lbs. beef cut into chunks
2 c. chopped onion or to taste
3 green peppers, chopped
1 (6 oz.) can tomato paste
1/2 c. brown sugar
1/2 c. vinegar
3 tbsp. chili powder or to taste
2 tsp. salt
2 tsp. Worcestershire sauce
1 tsp. dry mustard

Combine all ingredients and put in slow cooker and cook on high for 8 hours. With a wire whip stir meat until shredded. Serve on buns.