Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Submerge the chicken in buttermilk in a shallow bowl and marinate in the refrigerator for 30 minutes.
In a separate bowl, whisk together the arrowroot powder, almond flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the flour mixture, pressing to adhere.
Lightly spray or brush the breaded chicken with avocado oil and place in the air fryer basket.
Air-fry at 375°F for 12 to 15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
Mix the Greek yogurt and Dijon mustard in a small bowl to create a light, creamy sandwich spread.
Toast the whole-grain bun and assemble the sandwich by layering the sauce, lettuce, tomato, pickles, and the crispy chicken breast.