Preheat oven to 375° F. Spray a 12 cup muffin tin with non-stick spray.
In a large bowl, stir together 1/4 cup panko breadcrumbs, minced onion, parsley, parmesan cheese, garlic salt, pepper, minced garlic and egg. Stir until combined.
Add the ground chicken to the mixture, and gently combine (with your hands is easiest). Form the meatballs by rolling about 2 Tablespoons of chicken mixture in your hands, shaping into a ball. Press one cube of mozzarella cheese into the center of the meatball, and press mixture around it to hide cheese. Repeat with remaining chicken mixture and mozzarella.
Place the remaining panko breadcrumbs onto a large plate. Roll each meatball into the crumbs and then place in the muffin tin. You should get 12 meatballs total.
Bake meatballs for 20 to 25 minutes, or until fully cooked. Serve immediately with warm marinara sauce.