Place the chicken breast in a small bowl and pour the buttermilk over it; cover and marinate in the refrigerator for at least 30 minutes.
In a shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, and dredge it thoroughly through the flour mixture until evenly coated.
Lightly brush or spritz the breaded chicken on both sides with avocado oil.
Place the chicken in the air fryer basket and cook at 375°F (190°C) for 12-15 minutes, flipping halfway through, until the exterior is golden and 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 layering the lettuce, tomato, and pickles on the bottom bun, followed by the crispy chicken and the top bun.