1. Add all the ingredient A into a medium bowl and add the chicken to marinate at least 2 hours (or even overnight) in the fridge.
2. *Making Sauce :* In a bowl, add all the sauce ingredients and mix. Let is sit in the fridge until use.
3. Add flour and katakuriko/potato starch in a plate and roll the chicken pieces in it until coated.
4. Heat 2 to 3 cm vegetable oil in a large saucepan over medium heat. Carefully add 2 or 3 chicken pieces (depending on your saucepan's size) and deep-fry them, turning occasionally, until crisp and cooked through. Transfer them to a plate lined with paper towels to drain the excess oil. Continue with the rest of the chicken.
5. Toast the cut side of the burger buns lightly, and spread the sauce on the bottom half of the bun. Then place lettuce (or shredded cabbage), chicken. Add more sauce if you like. Cover with the top side bun.