Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Submerge the chicken in buttermilk in a shallow bowl and let it marinate for at least 15 minutes.
In a separate bowl, whisk together the whole wheat flour, smoked paprika, garlic powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the flour mixture until fully coated.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Cook the chicken for 4-5 minutes per side until the exterior is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
Lightly toast the whole grain bun in the same skillet or a toaster.
Assemble the sandwich by placing the chicken on the bottom bun, followed by the lettuce, tomato slices, and pickles.