Preheat the oven to 200°C (400°F). Line a baking sheet with aluminum foil and lightly spray it with cooking spray.

In a medium skillet, heat a drizzle of olive oil over medium heat. Add the finely diced onion and minced garlic, sauté for about 5 minutes until translucent.

In a large mixing bowl, combine ground chicken, cooled onion and garlic mixture, seasoned breadcrumbs, milk, grated Parmesan cheese, egg, chopped parsley, Italian seasoning, and salt. Mix gently until just combined.

Shape about two-thirds of the meat mixture into a rectangle on the prepared baking sheet, about 1 inch thick. Add the mozzarella cheese slices along the center and cover with the remaining meat mixture.

Spread marinara sauce over the top of the meatloaf. Bake for 45 minutes or until the internal temperature reaches 74°C (165°F).

Prepare the topping by combining panko breadcrumbs, extra grated Parmesan, melted butter, and chopped parsley in a small bowl.

After 45 minutes, remove the meatloaf from the oven. Sprinkle shredded mozzarella cheese and breadcrumb mixture on top. Return to the oven for an additional 15 to 20 minutes.

Let the meatloaf rest for about 10 minutes before slicing.