Place the chicken breast between two sheets of parchment paper and pound to an even thickness, then marinate in buttermilk for at least 30 minutes.
In a shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, and dredge thoroughly in the flour mixture, pressing to adhere.
Lightly coat the breaded chicken with avocado oil using a spray or brush to ensure a crispy finish.
Place the chicken in an air fryer basket and cook at 375°F for 12-15 minutes, flipping halfway through, until the coating is golden and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole grain bun in a dry pan or toaster.
Assemble the sandwich by placing the lettuce, tomato, and pickles on the bottom bun, followed by the crispy chicken fillet and the top bun.