In a large bowl or glass container, whisk the overnight buttermilk soak ingredients together, add the chicken breasts, cover, and soak overnight.
Remove the chicken breasts from the buttermilk mixture, discarding the liquid, and place them on a paper-towel-lined plate and set aside.
In a shallow bowl, whisk together: flour, salt, pepper, garlic powder, onion powder, and paprika until combined.
In a second shallow bowl, whisk the egg with 1 tbsp water. Then, pour the panko bread crumbs into a third shallow bowl.
Using a fork, dip the chicken breasts (one by one) into the flour mixture (let any excess buttermilk drip off before dipping-very important). Make sure to fully coat and shake off any excess flour, then into the egg wash (allowing any extra to drip off), and finally into the panko. Make sure to coat all sides thoroughly. Shake off any loose breading and place each breast onto a wire rack over a plate or small sheet pan. Once all of the chicken is breaded, place them into the refrigerator (on the wire rack) for 20 minutes. This helps the breading to bond to the meat and create a strong crust that doesn't fall apart.
Preheat the oven to 350 degrees F. and heat the avocado oil in a large cast-iron skillet over medium heat. When the heat reaches around 350 degrees, pan fry the breasts for about 3 minutes per side, until nice and golden.
Transfer the skillet to the oven and bake for 20 minutes. Test the chicken with a meat thermometer to ensure that a temperature of 165 degrees F. is reached before removing from the oven. I like to crank the heat up to broil for another couple of minutes to get the top nice and golden brown- just be sure to watch them closely so they don't burn! Serve with your favorite Southern sides.