1. Cut the chicken into large cuves and put in a bowl. Add the soy sauce, mirin, gingerroot, and garlic and turn the chicken to coat well. Cover with plastic wrap and let marinate in a cool place for 20 minutes.
2. Preheat a wok, then fill one-third full with oil, or use a deep-fryer. Heat the oil to 350-375 F/180-190 C, or until a cube of bread browns in 30 seconds.
3. Meanwhile, mix the potato starch with the salt in a bowl. Lift the chicken out of the marinade and shake off any excess. Drop it into the potato starch and coat well, then shake off any excess.
4. Add the chicken to the oil, in batches, and cook for 6 minutes, or until crisp and brown. Remove, drain on paper towels, and keep hot while you cook the remainging chicken.
5. Serve with lemon wedges.