Preheat your oven to 350°F (175°C) and prepare a loaf pan by greasing it or lining it with parchment paper.

In a large mixing bowl, combine the lean ground beef, breadcrumbs, diced onion, milk, egg, ketchup, Worcestershire sauce, fresh parsley, and seasonings. Mix thoroughly for 2-3 minutes.

Transfer the mixture into the prepared loaf pan, pressing down gently to remove air pockets and smooth the top.

In a small bowl, whisk together the ketchup, brown sugar, and apple cider vinegar for the glaze. Spread it generously over the meatloaf.

Bake in the preheated oven for approximately 55 minutes, or until the internal temperature reaches 160°F (71°C).

Remove from the oven and let it rest for 8-10 minutes before slicing.

Carefully slice the meatloaf and serve warm with your favorite sides.