Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a shallow bowl and pour the buttermilk over it, ensuring it is fully coated; let marinate for 15 minutes.
In a separate shallow dish, whisk together the arrowroot powder, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge it thoroughly in the arrowroot mixture until fully coated.
Lightly spray the breaded chicken on both sides with avocado oil.
Place the chicken in the air fryer basket and cook at 400°F for 12 to 15 minutes, flipping halfway through, until the coating is golden and crispy.
Toast the whole wheat bun in a dry pan or the air fryer for 1 minute until lightly browned.
Assemble the sandwich by placing the crispy chicken on the bottom bun, followed by the lettuce, tomato slices, and pickle chips.