Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness for uniform cooking.
Transfer the chicken to a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged, then marinate for at least 30 minutes in the refrigerator.
In a separate small 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, and dredge it thoroughly through the seasoned flour mixture.
Heat the olive oil in a non-stick skillet over medium heat and sear the chicken for 5-6 minutes per side until the exterior is golden-brown and the internal temperature reaches 165°F.
While the chicken rests, lightly toast the sourdough bun in the same skillet until the edges are crisp.
Assemble the sandwich by placing the lettuce on the bottom bun, followed by the crispy chicken, the dill pickles, and the top bun.