Preheat the oven to 375°F (190°C). Line a 9x5-inch loaf pan with parchment paper or lightly grease with non-stick cooking spray.
In a small bowl, combine Panko breadcrumbs and whole milk. Let sit for 5 minutes to form a panade, which ensures moisture retention in the lean chicken.
In a large mixing bowl, combine the ground chicken, panade mixture, grated Parmesan, beaten eggs, 4 minced garlic cloves, minced onion, parsley, and all dry seasonings (garlic powder, onion powder, Italian seasoning, salt, and pepper).
Gently mix the ingredients by hand until just incorporated. Avoid overworking the meat, as excessive handling will develop the proteins and result in a rubbery texture.
Transfer the mixture to the prepared loaf pan and smooth the top into an even layer, or shape into a free-form loaf on a lined baking sheet.
Bake for 40 minutes or until the internal temperature reaches 155°F (68°C) at the thickest part.
While the meatloaf is baking, prepare the glaze by whisking the melted butter with 2 cloves of finely minced garlic and the shredded Parmesan cheese.
Remove the meatloaf from the oven and brush the garlic-butter mixture evenly over the top. Return to the oven for an additional 10 minutes.
Optional: Switch the oven to broil for the last 2 minutes to achieve a golden-brown, crispy Parmesan crust.
Remove from the oven when the internal temperature reaches 165°F (74°C). Allow the meatloaf to rest for 10 minutes before slicing to allow the juices to redistribute.