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

In a skillet over medium heat, add a drizzle of olive oil, sauté the diced onion and minced garlic for 5 minutes or until softened and fragrant. Allow the mixture to cool completely.

Combine the cooled onion and garlic with ground chicken, seasoned breadcrumbs, milk, grated Parmesan cheese, egg, chopped parsley, Italian seasoning, and salt in a large mixing bowl. Gently mix everything together until just combined.

Transfer two-thirds of the meat mixture onto the prepared baking sheet and shape it into a rectangle. Create a well in the center and layer the mozzarella cheese strings inside. Spread the remaining meat mixture over the top, sealing in the cheese and shaping it into a loaf.

Spread a layer of marinara sauce over the top of the shaped meatloaf. Bake for 45 minutes until cooked through, reaching an internal temperature of 74°C (165°F).

Combine the panko breadcrumbs, additional Parmesan cheese, melted butter, and chopped parsley in a small mixing bowl. Set aside.

After the initial baking time, remove the meatloaf from the oven and add the mozzarella and panko breadcrumb topping. Bake for an additional 15-20 minutes until the topping is golden brown.

Allow the meatloaf to rest for about 10 minutes before slicing. Serve warm.