Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
In a shallow bowl, submerge the chicken in the buttermilk and let it marinate for at least 20 minutes in the refrigerator.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing excess to drip off, and dredge thoroughly in the flour mixture until well-coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Place the chicken in 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 wheat bun in a toaster or on a separate dry pan.
Assemble the sandwich by placing the romaine lettuce on the bottom bun, followed by the crispy chicken and dill pickles, then top with the remaining bun half.