Preheat air fryer to 375°F. Add a baking sheet or large plate next to the air fryer and sprinkle lightly with additional panko (or line with wax/parchment paper).
Hold your knife parallel to the cutting board and carefully slice the chicken from right to left (if you're a righty)... opening the chicken breast up like a book. Slice all the way through, so you now have 2 thinly sliced pieces of chicken. Repeat with other chicken breast.
Season chicken with salt and pepper on both sides.
Line up 2 shallow bowls next to the prepared baking sheet. In one of the bowls, add eggs, whisking until beaten. In the second bowl, add panko, Parmesan cheese, Italian seasoning and garlic powder, stirring together.
Add chicken, one piece at a time, to the egg mixture, turning to coat all sides, letting the excess drip off.
Next add the chicken to the breadcrumb mixture, turning and patting/pressing to coat all sides in the breadcrumbs.
Finally, transfer the chicken to the prepared baking sheet/plate. Repeat with all remaining chicken pieces.
Spray the basket of the air fryer with cooking spray (we like to use an olive oil spray), then place chicken breasts into the basket. You may be able to fit all 4 at once, or you may not; it will depend on the size of your air fryer.
Lightly spray tops of chicken breasts with cooking spray (this helps things get nice and crispy), then air fry for 6 minutes.
Flip chicken over and air fry another 5 minutes. Top each chicken breast with marinara sauce and mozzarella. Air fry another 3 minutes, or until cheese is melted and chicken reaches an internal temperature of 165°F.
Sprinkle with minced parsley or basil and serve on it's own, or over pasta.