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

In a medium skillet, add olive oil and sauté diced onion and minced garlic until soft and fragrant, about 5–7 minutes.

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

Shape two-thirds of the meat mixture into a rectangle on the baking sheet, creating a well in the center for the mozzarella.

Place mozzarella cheese strings in the well and encase them with the remaining meat mixture.

Spread marinara sauce over the top of the meatloaf. Bake for 45 minutes.

Mix panko breadcrumbs, grated Parmesan, melted butter, and parsley for the topping.

After 45 minutes, sprinkle shredded mozzarella and breadcrumb mixture on top and bake for another 15–20 minutes.

Let the meatloaf rest for about 10 minutes before slicing.