Place the chicken breast between two sheets of parchment paper and pound to an even 1/2-inch thickness.
In a shallow bowl, soak the chicken in buttermilk for at least 20 minutes to tenderize.
In a separate shallow dish, whisk together the flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, and dredge it through the flour mixture, pressing firmly to ensure a thick coating.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Place the chicken in the skillet and cook for 5 to 6 minutes per side until the coating is golden-brown and the internal temperature reaches 165°F.
Lightly toast the whole wheat bun in the skillet for the last minute of cooking.
Assemble the sandwich by placing the lettuce, tomato slices, and pickles on the bottom bun, followed by the crispy chicken and the top bun.