Place the chicken breast between two sheets of parchment paper and pound to an even 1/2-inch thickness using a meat mallet or rolling pin.
In a shallow bowl, submerge the chicken in the buttermilk and let it marinate for at least 15 minutes in the refrigerator.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge it thoroughly in the seasoned flour mixture until fully coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Carefully place the chicken in the skillet and cook for 4-5 minutes per side until the exterior is golden brown and the internal temperature reaches 165°F.
While the chicken rests for 2 minutes, lightly toast the whole wheat bun in the same skillet until the edges are crisp.
Assemble the sandwich by placing the lettuce leaf on the bottom bun, followed by the crispy chicken and the dill pickles.