Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a shallow bowl and pour the buttermilk over it, ensuring it is fully coated; let it marinate for at least 10 minutes.
In a separate shallow dish, whisk together the arrowroot powder, almond flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting any excess drip off, then dredge it thoroughly in the flour mixture, pressing the coating onto the meat.
Heat the avocado oil in a non-stick skillet over medium heat. Once hot, add the chicken and cook for 5-6 minutes per side until the crust is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken cooks, lightly toast the sprouted grain bun in a toaster or under the broiler.
Spread the Greek yogurt on the bottom bun, then layer with the romaine lettuce, tomato slices, and the crispy fried chicken breast before topping with the other half of the bun.