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 small bowl, whisk together the flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge thoroughly in the seasoned flour mixture.
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 until the coating is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, whisk together the Greek yogurt and Dijon mustard in a small ramekin to create a clean 'secret sauce'.
Lightly toast the whole wheat bun in the skillet or a toaster.
Spread the yogurt-mustard sauce on the bottom bun, top with the crispy chicken and dill pickles, and close the sandwich.