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 submerged; marinate for at least 20 minutes.
In a separate shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off, then dredge thoroughly in the flour mixture until well coated.
Preheat your air fryer to 375°F and lightly spray the air fryer basket with half of the avocado oil.
Place the chicken in the basket, spray the top of the chicken with the remaining avocado oil, and air fry for 12-15 minutes, flipping halfway through, until golden and cooked through.
Lightly toast the whole grain bun in a pan or toaster.
Assemble the sandwich by placing the crispy chicken on the bottom bun, followed by the lettuce, tomato slices, and pickles, then top with the other half of the bun.