Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged. Let it marinate for at least 20 minutes.
In a separate small bowl, whisk together the whole wheat flour, garlic powder, onion powder, sea salt, black pepper, and paprika.
Remove the chicken from the buttermilk, letting any excess drip off, and dredge it thoroughly in the flour mixture until evenly coated.
Preheat your air fryer to 375°F. Lightly spray the chicken on both sides with avocado oil and place it in the air fryer basket.
Air fry the chicken for 12 to 15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the exterior is golden and crisp.
While the chicken cooks, whisk together the Greek yogurt and Dijon mustard in a small ramekin to create the sandwich sauce.
Lightly toast the whole grain bun. Spread the yogurt sauce on the bottom half, then layer with lettuce, tomato, pickles, and the crispy chicken breast before topping with the other half of the bun.