In a large skillet, cook the ground beef, onion, and green bell pepper over medium heat until the beef is browned and the vegetables are tender. Drain off any excess grease.
Stir in the ketchup, brown sugar, Worcestershire sauce, mustard powder, salt, black pepper, and tomato sauce. Bring to a simmer and cook for at least 10 minutes, or until the sauce has thickened.
Serve the sloppy joe mixture on toasted hamburger buns.
Notes
For an extra kick, add a pinch of red pepper flakes to the sauce.