Place the chicken breast between two sheets of parchment paper and pound to an even thickness of about half an inch.
In a shallow bowl, soak the chicken in buttermilk for at least 15 minutes to tenderize.
In a separate bowl, whisk together the almond flour, arrowroot starch, garlic powder, onion powder, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess drip off, then dredge thoroughly in the flour mixture until fully coated.
Preheat your air fryer to 375 degrees Fahrenheit and lightly coat the basket with avocado oil spray.
Place the chicken in the basket, spray the top of the chicken with avocado oil, and air-fry for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165 degrees Fahrenheit.
Toast the whole wheat bun in the air fryer or a toaster until golden brown.
Assemble the sandwich by placing the crispy chicken on the bottom bun, topping with lettuce and tomato slices, and finishing with the top bun.