In a large skillet, over medium heat, add the ground beef and cook until browned, breaking it apart with a wooden spoon. Drain excess grease.
Add the chopped onion, bell pepper, and minced garlic to the skillet. Cook for about 5 minutes until the vegetables are softened.
Stir in the ketchup, brown sugar, Worcestershire sauce, Dijon mustard, chili powder, salt, and black pepper. Mix well until everything is combined.
Let the mixture simmer on low heat for about 10 minutes, stirring occasionally, until the sauce thickens and flavors meld.
While the mixture simmers, you can toast the hamburger buns if desired.
Serve the sloppy joe mixture on the toasted buns. Add sliced pickles or cheese if you like.