Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully coated. Let it marinate for at least 20 minutes.
In a small plate, combine the whole wheat flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess drip off, then dredge it through the flour mixture until evenly coated.
Preheat your air fryer to 375°F. Lightly brush or spray the chicken with avocado oil.
Air fry the chicken for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the exterior is golden and crispy.
While the chicken cooks, whisk together the Greek yogurt and Dijon mustard in a small bowl to create the sandwich sauce.
Toast the whole wheat bun lightly. Spread the yogurt sauce on both sides of the bun.
Assemble the sandwich by placing the shredded lettuce and pickles on the bottom bun, followed by the crispy chicken, and topping with the other half of the bun.