Place the chicken breast between two sheets of parchment paper and pound with a meat mallet to an even half-inch thickness.
In a shallow bowl, submerge the chicken in the low-fat 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, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing any excess to drip off, and dredge it thoroughly in the seasoned flour mixture until fully coated.
Heat the avocado oil in a non-stick skillet over medium-high heat until shimmering.
Carefully place the chicken in the skillet and cook for 5 to 6 minutes per side, or until the exterior is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken cooks, lightly toast the whole wheat bun in a toaster or under a broiler until the edges are crisp.
Assemble the sandwich by spreading the Greek yogurt on the bottom bun, then layering the lettuce, tomato, crispy chicken, and dill pickles before topping with the other bun half.