Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a shallow bowl and pour the buttermilk over it, turning to coat, and let marinate for 15 minutes.
In a separate shallow dish, whisk together the almond flour, arrowroot powder, garlic powder, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge in the flour mixture, pressing firmly so the coating adheres.
Heat the avocado oil in a medium non-stick skillet over medium heat.
Add the chicken to the skillet and cook for 5 to 6 minutes per side, or until the coating is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the sprouted grain bun in a toaster or under a broiler.
Assemble the sandwich by placing the lettuce and tomato on the bottom bun, followed by the crispy chicken and the dill pickles, then top with the remaining bun half.