Place the chicken breast in a shallow dish and pour the buttermilk over it, ensuring it is fully coated; marinate for at least 30 minutes in the refrigerator.
In a separate shallow bowl, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off, and dredge it through the flour mixture, pressing firmly to create a thick, even coating.
Lightly coat the breaded chicken with the avocado oil and place it in the air fryer basket.
Air fry at 375°F for 12 to 15 minutes, flipping halfway through, until the exterior is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, whisk the Greek yogurt and Dijon mustard together in a small bowl to create a creamy spread.
Toast the whole wheat bun in a dry pan or toaster until lightly browned and crisp.
Assemble the sandwich by spreading the yogurt sauce on the bun, then layering the lettuce, crispy chicken, and dill pickles.