Place the chicken breast in a shallow bowl and pour the buttermilk over it, letting it marinate for at least 15 minutes to tenderize.
In a separate small bowl, whisk together the whole wheat flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess liquid drip off, then dredge it thoroughly in the flour and spice mixture until evenly coated.
Lightly coat the air fryer basket with avocado oil and place the chicken inside, cooking at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden and crispy.
While the chicken cooks, stir the Greek yogurt and Dijon mustard together in a small ramekin to create a creamy, protein-packed sandwich spread.
Lightly toast the whole wheat bun, spread the mustard sauce on the bottom half, then layer with the lettuce, crispy chicken, and pickles before serving.