Brown the beef: In a large skillet over medium-high heat, brown the ground beef with the onion and bell pepper, breaking it up as it cooks, about 6-8 minutes. Drain off the excess grease.
Add the garlic: Stir in the garlic and cook for 1 minute until fragrant.
Build the sauce: Stir in the ketchup, tomato sauce, Worcestershire sauce, brown sugar, mustard, salt, and pepper.
Simmer: Reduce the heat to low and simmer, uncovered, for 10-15 minutes, stirring occasionally, until thickened.
Serve: Spoon onto hamburger buns and serve warm.
Notes
Let the sauce simmer the full 10-15 minutes uncovered, it thickens up and the sweet-tangy flavor balances out instead of tasting like straight ketchup.