Melt butter in a pan over medium heat. Add diced onion and bell pepper, cook for a few minutes until softened.
Add ground sirloin and cook, breaking it up well until browned.
Stir in black pepper, garlic powder, and seasoning blend.
Add Worcestershire sauce, fresh garlic, brown sugar, pureed tomatoes, ketchup, mustard, and apple cider vinegar. Mix everything well.
Lower the heat and let simmer for 18 minutes, stirring occasionally until thick.
Spoon onto toasted buns, add cheese if you like, and serve warm.
