Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
In a shallow bowl, submerge the chicken in buttermilk and let it marinate for at least 10 minutes.
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, letting excess drip off, and dredge thoroughly in the flour mixture, pressing down to ensure a thick coating.
Heat the avocado oil in a non-stick skillet over medium heat.
Add the chicken to the skillet and cook for 5 to 6 minutes per side until the crust is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken rests, lightly toast the sprouted grain bun in the same skillet or a toaster.
Assemble the sandwich by placing the lettuce and tomato on the bottom bun, followed by the crispy chicken and pickles, then top with the remaining bun half.