Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a bowl, pour over the buttermilk, and let marinate in the refrigerator for at least 30 minutes.
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, allowing excess to drip off, then dredge thoroughly in the flour mixture, pressing the coating into the meat.
Lightly coat the air fryer basket with avocado oil spray and place the chicken inside, spraying the top of the chicken with oil as well.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the crust is golden brown.
Lightly toast the whole grain bun and assemble the sandwich with the romaine lettuce, crispy chicken, and dill pickles.