For the sauce: In a medium bowl, stir together the ketchup, brown sugar, vinegar, mustard, Worcestershire sauce, salt and pepper. If not using fresh garlic, stir in the garlic powder, too. Make ahead tip: the sauce may be prepared in advance and refrigerated until ready to use.
Add the ground beef and onion to a 12-inch, nonstick or cast iron skillet set over medium heat. Cook, breaking up the beef as you go, until the meat is about two-thirds of the way browned. Add the red pepper and garlic, and continue cooking until the meat is cooked through and the peppers are beginning to soften, about 3 more minutes.
Stir in the sauce, bring the mixture to a simmer, and then decrease the heat to low and cook, uncovered, until the mixture is thick yet still a little goopy, about 15 minutes, stirring occasionally.
Serve and enjoy!