Prepare the Meatloaf Mixture: In a large bowl, combine the ground beef, onion, eggs, breadcrumbs, garlic, milk, Italian seasoning, parsley, salt, pepper, and 1/4 cup of ketchup. Mix gently with your hands or a wooden spoon until just combined. Avoid overmixing to keep the meatloaf tender.
Shape and Cook: Line your crockpot with tinfoil for easy cleanup. Place the meat mixture into the crockpot and shape it into a loaf. Cover and cook on high for 3 hours or on low for 6 hours.
Add the Glaze: Once the meatloaf is cooked, drain off any grease. Carefully lift the meatloaf out of the crockpot using the tinfoil and place it on a baking sheet.
Make the Glaze: In a small bowl, whisk together the ketchup, brown sugar, and Worcestershire sauce until well combined. Spread the glaze evenly over the meatloaf (you might have some left over for dipping).
Broil for Perfection: Place the meatloaf under the broiler for a few minutes until the glaze is bubbly and slightly caramelized.
Garnish and Serve: If desired, sprinkle with fresh parsley before serving.