Place the chicken breast between two sheets of parchment paper and pound with a meat mallet until it is an even half-inch thickness.
Place the chicken in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged; 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 excess to drip off, then dredge it thoroughly in the seasoned flour mixture until coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Add the chicken to the skillet and cook for 5-6 minutes per side, or until the exterior is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole grain bun in a toaster or on a separate dry pan.
Assemble the sandwich by placing the lettuce on the bottom bun, followed by the crispy chicken, dill pickles, and the top bun.