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 with the buttermilk and let it marinate for at least 15 minutes.
In a separate shallow dish, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing any excess to drip off, then dredge it thoroughly in the seasoned flour mixture until coated.
Heat the avocado oil in a cast-iron skillet over medium-high heat until shimmering.
Carefully place the chicken in the skillet and cook for 4-5 minutes per side until the crust is golden-brown and the internal temperature reaches 165°F.
While the chicken rests for a minute, lightly toast the sprouted grain bun in the same skillet.
Assemble the sandwich by placing the lettuce, tomato, and pickles on the bottom bun, followed by the crispy chicken and the top bun.