Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
In a shallow bowl, soak the chicken in buttermilk for at least 15 minutes to tenderize.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, and dredge thoroughly in the flour mixture until fully coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Add the chicken to the skillet and cook for 4-5 minutes per side, or until the exterior is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken rests for 2 minutes, lightly toast the whole wheat bun in the same skillet or a toaster.
Assemble the sandwich by placing the lettuce and tomato on the bottom bun, followed by the crispy chicken and dill pickles, then top with the remaining bun half.