Place the chicken breast between two sheets of parchment paper and pound with a meat mallet to an even 1/2-inch thickness.
Place the chicken in a shallow bowl and cover with the buttermilk, allowing it to soak for 10 minutes.
In a separate shallow dish, whisk together the almond flour, arrowroot starch, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, and dredge in the flour mixture, pressing firmly to ensure a thick, even coating.
Heat the avocado oil in a cast-iron skillet over medium-high heat until the oil is shimmering.
Carefully place the chicken in the skillet and sear for 4-5 minutes per side until the exterior is golden-brown and the internal temperature reaches 165°F.
While the chicken rests for 2 minutes, lightly toast the whole grain bun in the same skillet.
Assemble the sandwich by placing the lettuce on the bottom bun, followed by the crispy chicken and the dill pickles.