Begin by flattening the chicken breasts to an even thickness (about 1 inch) using a meat mallet or rolling pin. Season both sides with salt and pepper.
In one shallow bowl, beat the egg. In another shallow bowl, mix together the breadcrumbs, grated Parmesan cheese, Italian seasoning, and garlic powder.
Dip each chicken breast first into the beaten egg, ensuring it's well coated. Then transfer it to the breadcrumb mixture, pressing gently to adhere the crumbs to each side.
Preheat your air fryer to 375°F (190°C) for about 5 minutes.
Lightly spray the air fryer basket with cooking spray. Place the breaded chicken breasts in a single layer in the basket. Cook for 10 minutes, flipping halfway through.
After 10 minutes, carefully remove the basket. Spoon about ¼ cup of marinara sauce over each piece of chicken, then sprinkle shredded mozzarella on top.
Return the basket to the air fryer and cook for an additional 5-7 minutes or until the cheese is melted and bubbly.
Carefully remove the chicken from the basket. Let it rest for a couple of minutes before serving. Garnish with fresh basil leaves if desired.