1 1/2 pounds very lean ground beef
1 cup finely chopped onion
1 cup soft torn bread crumbs
2 teaspoons prepared mustard
1 teaspoon Worcestershire sauce
1 teaspoon dried parsley flakes
1 cup ketchup, divided
Spray crockpot with butter-flavored cooking spray. In a large bowl, combine ground beef, onion, egg, mustard, bread crumbs, Worcestershire sauce, parsley, and 1/2 cup ketchup. Shape mixture into a ball and place in slow cooker.
Spread remaining ketchup over top of loaf. Cover and cook on LOW for 6 to 8 hours.