Place each chicken breast between two sheets of plastic wrap or in a zip-top bag. Using a meat mallet or rolling pin, pound them evenly to about 1/4 inch thickness. This ensures they cook quickly and stay juicy.
Set up a breading station with three shallow dishes. In the first, combine the flour, salt, pepper, garlic powder, and paprika. In the second, whisk together the eggs and dijon mustard. In the third, toss together the plain breadcrumbs and panko breadcrumbs.
Dredge each pounded chicken breast in the seasoned flour, shaking off excess. Dip into the egg mixture, letting any extra drip off. Then press firmly into the breadcrumb mixture, coating both sides thoroughly.
Preheat the air fryer to 400 degrees F for 3 minutes.
Spray the air fryer basket with olive oil spray. Lay one or two schnitzels in the basket in a single layer without overlapping. Spray the top of each schnitzel generously with olive oil spray.
Air fry at 400 degrees F for 10 to 12 minutes, flipping once at the halfway mark and spraying the other side with oil. Cook until the crust is deep golden brown and the internal temperature reaches 165 degrees F.
Transfer to a cutting board and let rest for 2 minutes. Serve with a generous squeeze of lemon juice over the top and a sprinkle of fresh parsley.