Place the chicken breast between two pieces of parchment paper and pound to an even thickness of about half an inch.
Submerge the chicken in a bowl with the buttermilk and let it marinate for at least 15 minutes to tenderize.
In a shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the flour mixture until fully coated.
Lightly coat the air fryer basket with avocado oil, place the chicken inside, and spritz the top of the chicken with the remaining oil.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
Toast the whole grain bun until lightly browned, then assemble the sandwich with the lettuce, crispy chicken, and dill pickles.