Place the chicken breast between two pieces of parchment paper and pound to an even half-inch thickness to ensure even cooking.
Submerge the chicken in a bowl with the buttermilk and let it marinate for at least 15 minutes to tenderize the meat.
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 excess drip off, then dredge thoroughly in the flour mixture until fully coated.
Lightly coat the air fryer basket with half of the avocado oil, place the chicken inside, and drizzle the top of the chicken with the remaining oil.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the coating is golden and the internal temperature reaches 165°F.
Toast the bun until warm and slightly golden, then spread with Dijon mustard and layer with lettuce, tomato, pickles, and the crispy chicken.