Heat a large skillet over medium-high heat and add the ground beef, breaking it up with a wooden spoon as it cooks.
Cook the beef for 5 to 6 minutes until no pink remains, then drain any excess fat from the pan.
Reduce the heat to medium and add the diced onion and bell pepper to the pan with the beef.
Cook, stirring occasionally, for 4 to 5 minutes until the vegetables have softened.
Add the garlic and cook for 1 minute, stirring, until fragrant.
Stir in the ketchup, tomato sauce, Worcestershire sauce, brown sugar, mustard, apple cider vinegar, chili powder, garlic powder, salt, and black pepper.
Stir everything together until the beef is fully coated in the sauce, then reduce the heat to low and simmer for 10 minutes, stirring occasionally, until the sauce has thickened and the flavors have come together.
Taste and adjust seasoning, adding more brown sugar for sweetness, vinegar for tang, or chili powder for heat.
Spoon the filling generously over toasted buns and serve immediately.