Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a shallow bowl with the buttermilk and marinate for at least 30 minutes in the refrigerator.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess drip off, then dredge in the flour mixture, pressing firmly to ensure a thick, even coating.
Lightly mist the chicken on both sides with avocado oil and place in the air fryer basket.
Air-fry at 400°F for 12 to 15 minutes, flipping halfway through, until the coating is golden brown and the internal temperature reaches 165°F.
In a small bowl, stir together the Greek yogurt and Dijon mustard to create a clean, tangy sandwich spread.
Toast the whole wheat bun until lightly browned, spread the yogurt-mustard sauce on both sides, and assemble with the crispy chicken and dill pickles.