In a container with a lid, or a sturdy sipper-top plastic bag, combine the olive oil, lemon juice, mustard, garlic, red pepper flakes and salt and pepper. Stir4 or squish to blend the ingredients. Add the chicken and turn to coat well. Seal the bag or container and refrigerate for 8 to 24 hours (the longer you marinate it, the more pronounced the flavors would be).
Set up your air fryer. Remove the chicken from the marinade and place it in a single layer in the basket or insert. Set the temperature for 400°F if you have a choice, dual heat, and set the timer for 10 minutes. After 10 minutes, check to see if the chicken is cooked through (165°F internal temperature). Let the chicken sit on a cutting board or plate for 2 minutes before serving. Slice if desired.