Preheat the air fryer to 360°F (182°C) for 5 minutes.
Using a sharp knife, cut a deep pocket lengthwise into each chicken breast without cutting through to the other side.
Divide the mozzarella slices: cut each slice in half if needed, then stuff each chicken pocket with two halves (one whole slice worth) of mozzarella and 4 fresh basil leaves per breast.
Secure the openings with toothpicks to keep the filling inside.
In a shallow bowl combine Panko, Italian seasoning, garlic powder, grated Parmesan, kosher salt, and black pepper.
Place the flour in a second shallow bowl and the beaten eggs in a third bowl.
Dredge each stuffed chicken breast first in flour, shaking off excess, then dip into the beaten eggs, and finally press into the Panko mixture to coat evenly on all sides.
Arrange the coated chicken breasts in a single layer in the air fryer basket without overcrowding.
Cook at 360°F for 20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
When cooking is complete, spoon marinara sauce over each breast and top with the remaining mozzarella slice (cut if needed), then air fry for 1 additional minute until the cheese melts.
Remove toothpicks, garnish with sliced fresh basil if using, and serve.