Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
In a shallow bowl, submerge the chicken in buttermilk and let it marinate for at least 15 minutes.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off, then dredge thoroughly in the flour mixture, pressing to adhere.
Lightly spray the breaded chicken with avocado oil and place in an air fryer basket at 375°F.
Air-fry for 12-15 minutes, flipping halfway through, until the exterior is crispy and the internal temperature reaches 165°F.
While the chicken cooks, stir together the Greek yogurt and Dijon mustard in a small bowl to create a healthy spread.
Lightly toast the whole wheat bun, spread the yogurt sauce on both sides, and assemble with the crispy chicken and dill pickles.