Preheat the oven to 350°F. Spray a 9x5-inch loaf pan with nonstick cooking spray. Set aside.
To a large bowl, add ground beef, ground pork, parsley, salt, pepper, garlic powder, and beaten egg. Mix together until just combined. (I prefer to use my hands to mix, but a spoon or spatula would also work.)
In a medium bowl, combine the milk, breadcrumbs, and onion.
Add milk mixture to the meat mixture being careful not to overwork ingredients.
Add the meat mixture to the prepared loaf pan, pressing the meat in tightly.
Bake for 60-65 minutes, or until no longer pink in the center. The meatloaf is fully cooked when it reaches an internal temperature of 160°F.
During the final 5-10 minutes of cooking the meatloaf, prepare the gravy.