In a large skillet over medium heat, brown the ground beef with the chopped onion until the meat is fully cooked and the onion is soft. Drain excess grease if needed.
Stir in the ketchup, mustard, sugar, vinegar, and Worcestershire sauce.
Season with salt and pepper.
Reduce heat and let the mixture simmer for 15-20 minutes, stirring occasionally, until thick and saucy.
Spoon onto buns and serve warm.
Notes
Nutrition will vary depending on meat fat content and bun choice.