Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness to ensure even cooking.
Place the chicken in a shallow bowl with the buttermilk and marinate for at least 30 minutes in the refrigerator.
In a separate shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off, then dredge thoroughly in the flour mixture, pressing to adhere.
Lightly brush or spray the coated chicken with avocado oil and place in an air fryer basket.
Air fry at 375°F for 12 to 15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the coating is golden brown.
Toast the whole wheat bun in a dry pan until lightly browned and fragrant.
Assemble the sandwich by placing the romaine lettuce, crispy chicken, and dill pickles on the toasted bun.