Place the chicken breast between two sheets of parchment paper and pound to an even thickness of about half an inch.
In a shallow bowl, soak the chicken in the buttermilk for at least 15 minutes to tenderize.
In a separate shallow dish, 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 seasoned flour mixture.
Heat the avocado oil in a non-stick skillet over medium-high heat.
Add the chicken to the skillet and cook for 5-6 minutes per side until the coating is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken cooks, stir together the Greek yogurt and Dijon mustard in a small bowl to create the sauce.
Lightly toast the whole wheat bun in the skillet or a toaster.
Assemble the sandwich by spreading the yogurt sauce on the bottom bun, followed by the lettuce, tomato, crispy chicken, and pickles.