In a large mixing bowl, combine the pounded garlic, cilantro roots (or stems), sea salt, fish sauce, oyster sauce, and ground black pepper. Add the chicken pieces and mix well to coat. Cover with plastic wrap and let marinate in the refrigerator for at least 2 hours, preferably overnight.
In a separate bowl, mix the all-purpose flour, cornstarch, and rice flour together.
In a deep fryer or heavy pot, heat enough oil to submerge the chicken pieces (about 3-4 inches deep) to 350°F (175°C).
Once the chicken has marinated, remove it from the refrigerator. Take each piece and dredge it in the flour mixture, ensuring an even coating. Shake off any excess flour.
Carefully place the coated chicken pieces into the hot oil, a few at a time to avoid overcrowding. Fry for about 8-10 minutes or until golden brown and cooked through.
Once cooked, use a slotted spoon to remove the chicken from the oil and place it on a plate lined with paper towels. Serve hot with your favorite dipping sauces.