Mix 2 tbs. of the TexMex Spice Rub with the buttermilk. Place chicken and buttermilk mixture into a resealable bag, and marinate in the refrigerator for at least 2 hours (overnight works best).
In separate dishes, lay out the flour, whisked eggs, and panko breadcrumbs. Season each piece of meat to taste with salt and pepper.
Remove chicken from the buttermilk, and let the excess drip off the chicken. Place each piece into the seasoned flour mixture, and shake off the excess flour. Dip into the whisked eggs, then into the panko breadcrumbs so that each piece is fully coated. Repeat for each piece of chicken. Refrigerate for 30 minutes before cooking.
In a medium pan, heat the oil on medium high heat until the oil reaches 350 degrees. Drop the chicken carefully into the oil, and allow to cook for at least 5 minutes on each side. Transfer to a wire rack to allow excess oil to drip off.
Mix 1 tablespoon of the TexMex Spice Rub into 2 tablespoons of mayo to make up the sauce. Toast the hamburger buns, place a piece of chicken on each, spread with mayo, then add your toppings.