Lay your ultra thin chicken breasts on a large cutting board. Season them on both sides with the salt, garlic powder, and black pepper.
Add a slice of ham and cheese to each chicken breast and roll up the chicken You can use toothpicks to hold it in place. I keep my toothpicks on even in the air fryer.
Coat the chicken roll ups in panko breadcrumbs. Push the breadcrumbs into the chicken making sure to cover it completely.
Spray the inside basket of your air fryer with cooking oil. Place the chicken cordon blue in your air fryer basket and spray the top of the chicken with cooking oil. Cook at 390F for 25-28 minutes. Let the chicken rest of 5 minutes before cutting into it.
While your chicken is cooking, make your sauce in a small saucepan on the stove. Heat the butter and when it is melted, add your flour. Using a whisk, mix the flour and butter until fully incorporated and heat on low heat for 1 minute. Add your milk and bring the heat up to medium, stirring frequently. Once the milk starts to bubble, turn off the heat, add in the dijon, cheese, garlic powder, salt, and pepper. Keep stirring until the mixture thickens. It will continue to thicken as it cools too. If it gets too thick, add in a little more milk to thin it out.