In a large bowl, stir together meat, green pepper, onion, bread crumbs, 1/4 cup of the ketchup, parsley, milk, Worcestershire, salt and pepper until well blended.
Fit a long piece of foil into oval slow cooker so ends are hanging over sides and press into place. Spoon meatloaf mixture onto foil and form into an oval-shaped loaf. Spread remaining 3 tablespoons of ketchup over top of meat mixture.
Cover and cook on HIGH for 3 hours or LOW for 6 hours, or until internal temperature registers 160° F on an instant-read thermometer.
To serve, carefully lift meatloaf out of slow cooker using foil handles. Slice using a serrated knife and serve immediately.