Place the chicken breast between two sheets of parchment paper and pound with a meat mallet until it is an even 1/2-inch thickness.
In a shallow bowl, soak the chicken in buttermilk for at least 15 minutes to tenderize.
In a separate shallow dish, 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, and dredge thoroughly in the flour mixture, pressing the coating firmly onto the meat.
Preheat the air fryer to 375°F and lightly spray or brush the chicken with avocado oil.
Air fry the chicken for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the exterior is golden brown.
Lightly toast the sprouted grain bun in a dry pan or the air fryer for 1 minute.
Assemble the sandwich by placing the crispy chicken on the bottom bun, followed by the lettuce, tomato slices, and pickles, then top with the remaining bun half.