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 the buttermilk for at least 15 minutes to tenderize.
In a separate small bowl, whisk together the whole wheat flour, garlic powder, onion powder, 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.
Lightly spray or brush the breaded 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 golden brown and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole 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.