Place the chicken breast between two pieces of parchment paper and pound to an even thickness of about half an inch.
In a small bowl, submerge the chicken in the buttermilk and let it marinate for at least 15 minutes in the refrigerator.
In a shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, and dredge it thoroughly in the seasoned flour mixture until coated.
Place the chicken in the air fryer basket and generously coat both sides with the avocado oil spray.
Air fry at 375°F for 12 to 15 minutes, flipping the chicken halfway through, until the coating is golden brown and the internal temperature reaches 165°F.
While the chicken is cooking, whisk together the Greek yogurt and Dijon mustard in a small bowl to create a healthy sandwich spread.
Lightly toast the whole wheat bun in a toaster or on a dry pan until warm and slightly crisp.
Assemble the sandwich by spreading the yogurt sauce on both sides of the bun, then layering the lettuce, crispy chicken, and dill pickles.