Pour the buttermilk into a dish. In another dish, combine the panko, paprika, garlic powder, onion powder, sea salt and freshly cracked pepper, to taste; mix until well combined. Dip the chicken into the buttermilk then dip into the panko crumb mixture until evenly coated. Place the coated chicken onto the baking rack lined baking sheet; repeat with the remaining chicken thighs. Season the top of the crusted chicken thighs with a little more sea salt and freshly cracked pepper, to taste, then spray with cooking spray.