Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness to ensure quick and even cooking.
Submerge the chicken in a small bowl with the buttermilk and let it marinate for at least 20 minutes to tenderize the meat.
In a shallow dish, whisk together the flour, smoked paprika, garlic powder, sea salt, and black pepper until well combined.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge thoroughly in the flour mixture until fully coated.
Lightly mist both sides of the coated chicken with avocado oil and place it in the air fryer basket.
Air fry at 400°F for 12-15 minutes, flipping halfway through, until the exterior is golden brown and the internal temperature reaches 165°F.
Toast the whole wheat bun until warm and assemble the sandwich by layering the lettuce, tomato slices, pickles, and the crispy chicken.