Add onions to the pan; cook, stirring often, until onion is softened, about 5 minutes. Add chili powder, garlic powder, onion powder, and cayenne; cook, stiring constantly, until fragrant, about 30 seconds. Stir in tomato sauce, ketchup, worcestershire, mustard and brown sugar. Return the beef to the pan. Bring to a simmer and cook, stirring often, until the beef is just cooked through and the sauce has thickened slightly, about 5 minutes. Serve on open face bun.