Place the chicken breast between two sheets of parchment paper and pound to an even 1/2-inch thickness.
In a shallow bowl, soak the chicken in the low-fat buttermilk for at least 15 minutes to tenderize.
In a separate shallow dish, whisk together the almond flour, arrowroot starch, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk and dredge it in the flour mixture, pressing firmly to ensure a thick, even coating on all sides.
Lightly brush or spray the coated chicken with avocado oil and place it in the air fryer basket.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
Toast the whole grain bun in a pan or toaster until warm and lightly browned.
Assemble the sandwich by placing the romaine lettuce on the bottom bun, followed by the crispy chicken and dill pickles.