In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the finely diced onion and minced garlic, sautéing until softened and fragrant, about 5-7 minutes. Once cooked, transfer them to a bowl and let them cool completely.

In a mixing bowl, combine the ground chicken, cooled onion and garlic mixture, seasoned breadcrumbs, milk, grated Parmesan cheese, egg, chopped parsley, Italian seasoning, and salt. Mix until well blended, being careful not to overmix.

Prepare a baking sheet by lining it with aluminum foil. Press two-thirds of the meat mixture into a rectangular shape. Create a slight indentation down the center, layer sliced mozzarella cheese inside, and cover with remaining chicken mixture, sealing the edges.

Preheat your oven to 200°C (400°F). Spread marinara sauce over the top of the shaped meatloaf. Bake for about 45 minutes, or until golden and the internal temperature reads 74°C (165°F).

Prepare the crunchy topping by mixing panko breadcrumbs, grated Parmesan cheese, melted butter, and chopped parsley. After 45 minutes, sprinkle with shredded mozzarella cheese followed by the breadcrumb mixture.

Return the meatloaf to the oven and bake for an additional 15-20 minutes, until the breadcrumbs are golden brown. Let it rest for 10 minutes before slicing.