Place the chicken breast between two pieces of parchment paper and pound to an even half-inch thickness.
Submerge the chicken in a shallow bowl with the buttermilk and let it marinate for at least 15 minutes.
In a separate wide dish, whisk together the almond flour, arrowroot powder, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge thoroughly in the flour mixture until well-coated.
Heat the avocado oil in a large non-stick skillet over medium heat until shimmering.
Carefully place the chicken in the skillet and cook for 5 to 6 minutes per side until the crust is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole grain bun in a toaster or under a broiler.
Build the sandwich by placing the lettuce, tomato, and pickles on the bottom bun, topping with the crispy chicken, and closing with the top bun.