Place the chicken breast in a small bowl with the buttermilk and marinate for at least 30 minutes in the refrigerator.
In a shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess liquid drip off, then dredge it thoroughly in the seasoned flour mixture.
Lightly coat the breaded chicken with avocado oil using a mister or brush, then place in the air fryer basket.
Air-fry at 400°F for 12-15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
Lightly toast the whole wheat sandwich thin until warm and slightly browned.
Assemble the sandwich by placing the crispy chicken on the bottom bun, followed by the lettuce, tomato slices, and pickles before topping with the other bun half.