Preheat the air fryer for five minutes at 380 degrees. Get a cookie cooling rack out for later.
Use a sharp knife to cut the chicken into bite-sized pieces. I like about 1 1/2-2-inch bites. Pat the chicken pieces dry with a paper towel. Sprinkle the chicken on all sides with salt and pepper.
In a shallow bowl or dish, whisk the egg with water. Add the flour, cornstarch and salt to a large ziplock bag. Seal shut and shake to combine.
Working in two batches, add half of the chicken to the egg mixture. Use tongs to coat the chicken in the egg. Use the tongs to pick up the chicken and let any excess egg drip off. Transfer the chicken to the ziplock bag. Shake the bag until the chicken is coated. Repeat with remaining chicken.
Spray the bottom of the air fryer with olive oil spray. Place half of the chicken in the bottom of the air fryer. Be sure there is some space in between each piece of chicken. Spray the top of the chicken with olive oil spray. There should be no dry flour spots.
Set the temperature to 380 degrees and the time for 5 minutes. Press start. After five minutes, flip chicken over and spray the other side of the chicken with olive oil spray. Set the temperature for 400 degrees for another 3-4 minutes. (The total amount of time will depend on the size of your chicken pieces.) The chicken is done when the exterior is crisp and the interior is 165 degrees. Transfer chicken to a cookie cooling rack. Repeat process with remaining chicken.
While the chicken cooks, make the sauce. Gather all your ingredients for the sauce. Add the orange juice, soy sauce, mirin, brown sugar, crushed red pepper flake, chicken stock, rice vinegar and cornstarch to a small bowl. Whisk to combine.
Heat a large skillet to a medium heat. When the skillet is hot, add the sesame oil. Swirl to coat the bottom of the pan. Add the garlic and ginger. Sweat the garlic and ginger until fragrant and soft, about 1-2 minutes. If either starts to brown, turn the heat down to medium low.
Whisk in the sauce. Bring to a boil and reduce to a simmer. Simmer until the sauce is thick, about 2-3 minutes. Season to taste with salt and pepper. Turn the heat off and set aside until the chicken is done cooking.
When all of the chicken is cooked, return the skillet to a low heat. Add the chicken. Toss to coat. Serve sprinkled with green onion.