Place the chicken breast between two pieces of parchment paper and pound to an even half-inch thickness for uniform cooking.
In a shallow bowl, submerge the chicken in the buttermilk and let it marinate for at least 15 minutes to tenderize.
In a separate bowl, whisk together the almond flour, arrowroot starch, garlic powder, onion powder, paprika, salt, and pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the flour mixture, pressing firmly to adhere.
Lightly coat the air fryer basket with half of the avocado oil, place the chicken inside, and spritz the top with the remaining oil.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the coating is golden-brown and the internal temperature reaches 165°F.
Toast the whole wheat bun until warm and assemble the sandwich with the crispy chicken, lettuce, tomato slices, and pickles.