Preheat your oven to 200°C (400°F) and prepare a baking sheet by lining it with aluminum foil and spraying it lightly with cooking spray.

In a medium-sized skillet, heat a tablespoon of olive oil over medium heat. Add the finely diced onion and minced garlic, sautéing them until softened and fragrant, about 5 minutes.

In a large mixing bowl, combine the ground chicken, sautéed onion and garlic, seasoned breadcrumbs, milk, grated Parmesan cheese, egg, chopped parsley, Italian seasoning, and salt. Gently mix until just combined.

Using two-thirds of the meat mixture, form a rectangle in the center of your baking sheet. Create a well in the middle to place the mozzarella cheese strings.

Spread a generous amount of marinara sauce over the top of the assembled meatloaf.

Place the meatloaf in the preheated oven and bake for 45 minutes.

While the meatloaf bakes, prepare the topping by mixing panko breadcrumbs, melted butter, grated Parmesan cheese, and chopped parsley in a small bowl.

After the initial baking, sprinkle the breadcrumb mixture evenly over the top, then add shredded mozzarella cheese. Return it to the oven for an additional 15-20 minutes.

Once fully cooked, remove the meatloaf from the oven and let it rest for 10 minutes before slicing.