Slice each chicken breast horizontally to make four thinner pieces; season both sides generously with kosher salt and freshly ground black pepper.
In a shallow dish, mix all-purpose flour with a pinch of kosher salt and some freshly ground black pepper. In another bowl, whisk the eggs thoroughly. Combine panko, grated Parmesan, dried oregano, crushed red pepper flakes, and garlic powder in a third shallow bowl.
One piece at a time, dredge the chicken first in the flour mixture, shaking off excess, then dip into the beaten eggs, letting extra drip off. Finally, press the chicken into the panko blend, coating each side firmly.
Arrange coated chicken pieces in a single layer inside the air fryer basket. Cook at 400°F for about 5 minutes, then flip and cook an additional 5 minutes until cooked through. Spoon marinara sauce on top of each piece and sprinkle with mozzarella cheese. Return to the air fryer and cook for another 3 minutes or until the cheese is melted and golden.
Garnish with chopped fresh parsley before serving.