Place the chicken breast in a shallow bowl and cover with buttermilk; marinate for at least 15 minutes in the refrigerator.
In a separate small bowl, whisk together the whole wheat flour, paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge it thoroughly in the seasoned flour mixture until evenly 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 degrees Fahrenheit.
While the chicken cooks, lightly toast the whole grain bun in a toaster or on a separate dry pan.
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.