Pound the chicken breast to an even thickness and marinate in buttermilk for at least 30 minutes in the refrigerator.
In a shallow bowl, whisk together the almond flour, arrowroot starch, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge in the flour mixture, pressing firmly to ensure an even coating.
Lightly brush or spray the coated chicken with avocado oil and place in the air fryer basket.
Air-fry at 375°F for 12-15 minutes, flipping halfway through, until the exterior is crispy and the internal temperature reaches 165°F.
Toast the whole grain bun and assemble the sandwich by layering the butter lettuce, tomato slices, pickles, and the crispy chicken.