Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged; marinate for at least 30 minutes in the refrigerator.
In a separate small bowl, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge it thoroughly in the seasoned flour mixture until evenly coated.
Lightly spray or brush the breaded chicken with avocado oil to ensure a crispy texture during cooking.
Place the chicken in the air fryer basket and cook at 375°F for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole wheat bun in a dry pan or toaster.
Assemble the sandwich by placing the crisp lettuce and dill pickles on the bottom bun, topping with the hot chicken, and closing with the top bun.