Place the chicken breast between two sheets of parchment paper and pound with a meat mallet to an even half-inch thickness.
Transfer the chicken to a shallow bowl and cover with buttermilk, allowing it to marinate for at least 15 minutes in the refrigerator.
In a separate shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge it through the flour mixture, pressing firmly to create a thick crust.
Lightly coat the breaded chicken with avocado oil and place it 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.
Toast the whole grain bun until warm and assemble the sandwich with the crispy chicken, lettuce, tomato slices, and pickles.