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 (using your hands is the easiest).
Form the meatballs by rolling 3 Tablespoons of chicken mixture in your hands, shaping into a ball. (I use a measuring spoon and measure precisely 3 Tablespoons per meatball.) Press one cube of mozzarella cheese into the center of the meatball; pressing mixture around it to hide the cheese. Repeat with remaining chicken mixture and mozzarella cheese.
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 10 to 11 meatballs total.
Bake meatballs, uncovered, for 22 to 25 minutes or until fully cooked. Serve meatballs warm with warm marinara sauce. Enjoy!