Preheat your oven to 200°C (400°F) and line a baking sheet with parchment paper.

In a skillet over medium heat, sauté the finely diced onion and minced garlic in olive oil until softened.

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

Transfer about two-thirds of the meat mixture onto the baking sheet and shape it into a loaf, creating a well in the center.

Stuff the well with mozzarella cheese strings and seal them with the reserved 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).

While the meatloaf bakes, combine panko breadcrumbs, Parmesan, butter, and parsley in a bowl.

After 45 minutes, sprinkle shredded mozzarella and the panko mixture over the top. Bake for an additional 15–20 minutes.

Let the meatloaf rest for 10 minutes before slicing to allow juices to redistribute.