Place the chicken breast between two sheets of parchment paper and pound with a meat mallet to an even thickness.
In a shallow bowl, whisk together the buttermilk, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Submerge the chicken breast in the buttermilk mixture and let it marinate for at least 15 minutes to tenderize.
Dredge the marinated chicken in the whole wheat flour, pressing firmly to ensure an even coating on all sides.
Lightly coat the air fryer basket with olive oil and place the chicken inside, brushing the top of the chicken with any remaining oil.
Air fry at 375°F for 12 to 15 minutes, flipping halfway through, until the coating is golden and the chicken is cooked through.
In a small bowl, combine the nonfat Greek yogurt and Dijon mustard to create a tangy sandwich spread.
Toast the whole grain bun until light brown, spread the yogurt sauce on both sides, and assemble with the crispy chicken, lettuce, and tomato slices.