Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a shallow bowl and pour the buttermilk over it, ensuring it is fully coated, and let it marinate for 15 minutes.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess drip off, then dredge it in the flour mixture, pressing firmly so the coating adheres.
Lightly brush or spray the breaded chicken on both sides with avocado oil.
Place the chicken in the air fryer basket and cook at 375°F for 12 to 15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
During the last 2 minutes of cooking, place the split bun in the air fryer to lightly toast.
Assemble the sandwich by placing the lettuce on the bottom bun, followed by the crispy chicken and dill pickles.