Heat a large skillet over medium heat.
Add the ground beef and cook until fully browned, breaking it apart as it cooks.
Drain excess grease from the pan.
Add the chopped onion and bell pepper and cook for 3–4 minutes until softened.
Stir in the garlic and cook for about 30 seconds until fragrant.
Add the ketchup, tomato sauce, Worcestershire sauce, brown sugar, and mustard.
Season with salt and black pepper.
Reduce heat to low and let the mixture simmer for 10–15 minutes, stirring occasionally, until thick.
Spoon the sloppy joe mixture onto buns and serve warm.
