Heat olive oil in a skillet over medium heat, add diced onion and minced garlic, sautéing until softened, about 5 minutes. Remove from heat and cool completely.

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

On a parchment-lined baking sheet, form ⅔ of the chicken mixture into a rectangle, then place mozzarella cheese strings in the center. Mold the remaining mixture on top to seal the cheese.

Preheat oven to 200°C (400°F). Spread marinara sauce over meatloaf and bake for 45 minutes until cooked through.

Mix panko breadcrumbs, Parmesan, melted butter, and parsley. Remove meatloaf, add mozzarella on top, and sprinkle breadcrumb mixture. Return to oven for 15-20 minutes until golden brown.

Let meatloaf rest for 10 minutes before serving with extra marinara on the side.