Lightly spray a 2 to 4 quart slow cooker with nonstick spray.
Pour the buttermilk into a small mixing bowl. In another bowl, combine the flour, black pepper, paprika, garlic powder, and kosher salt. Add the panko bread crumbs to a shallow dish.
Dip the chicken breast into the buttermilk and allow the excess to drip off. Dredge the filet into flour mixture before dipping it again into the buttermilk.
Press the chicken breast into the panko, pressing it gently into the breadcrumbs on each side to make sure they adhere.
Mist the chicken on both sides with nonstick cooking spray and place it in the slow cooker.
Cover and cook on high 2-1/2 hours or until the chicken has reached an internal temperature of 165 degrees.
Remove the lid and allow to continue cooking for 10 minutes. Removing the lid helps the chicken get crunchier.