Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged for at least 20 minutes.
In a separate small bowl, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge it thoroughly in the flour mixture until evenly coated.
Lightly coat the air fryer basket with avocado oil and place the chicken inside, spraying 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 and assemble the sandwich with the lettuce, tomato slices, pickles, and the crispy chicken.