Combine the ground beef and onions in a large skillet and cook over medium heat, breaking up the chunks with a wooden spoon, until the meat is browned, about 10 minutes. Drain off the excess fat. In a small mixing bowl, stir together the ketchup, brown sugar, vinegar, Worcestershire, mustard, and honey if using until well combined. Stir the sauce mixture into the meat and onions and bring to a simmer. Serve on hamburger buns.