Preheat your air fryer to 350°F (175°C).
Place the boneless, skinless chicken breasts on the cutting board. Using a sharp knife, slice them in half and pound each piece to 1-inch thickness using a meat mallet or a rolling pin. Season both sides of your thin cutlets with salt and pepper.
In a shallow bowl, combine the beaten eggs, water, onion powder, garlic powder, and cornstarch. I recommend adding tablespoon at a time if the batter is too thick.
In a separate shallow bowl, place the panko breadcrumbs.
Dip the seasoned chicken cutlets into the beaten egg and cornstarch mixture, coating both sides. Then transfer the chicken from the wet batter to the panko mixture, pressing the crispy panko breadcrumbs onto both sides to ensure an even coating.
Spray the coated chicken breasts with minimal olive oil cooking spray on both sides and then place the chicken in the preheated air fryer basket in a single layer, making sure not to overcrowd. Cook for 7-9 minutes, then flip the chicken and cook for an additional 7-9 minutes, or until the chicken is crispy and golden brown.
Remove each piece of crispy chicken from the air fryer and let it cool for 4-6 minutes before serving.
Enjoy your crispy and delicious air fryer katsu!