Place the chicken breast between two sheets of parchment paper and pound to an even thickness.
In a shallow bowl, whisk together the buttermilk, garlic powder, onion powder, sea salt, and black pepper.
Submerge the chicken in the buttermilk mixture and let it marinate for at least 15 minutes.
Place the whole wheat flour in a separate shallow dish and dredge the marinated chicken until lightly coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Cook the chicken for 5 to 6 minutes per side until the exterior is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, lightly toast the whole wheat bun in a dry pan or toaster.
Assemble the sandwich by placing the lettuce on the bottom bun, followed by the crispy chicken, pickles, and the top bun.