In a frying pan, brown the beef and onions together. While the beef is cooking, add the chili powder, dried chili flakes, garlic powder and salt and pepper.
Transfer the beef to the slow cooker. Add the diced pepper, mustard, brown sugar, ketchup, vinegar, and Worcestershire sauce. Mix well
Cook on low for 4 – 5 hours. Watch the mixture as it cooks, and add water to the mix if it seems to be getting a bit thick.
After cooking time is complete, toast buns and put the mixture on top of the bread. You can also garnish it with shredded cheese if you prefer.
Notes
You can easily change the spiciness of this recipe by varying the amount of dried chili flakes and chili powder.