Combine garlic, ginger, soy and vinegar in a bowl. Cut chicken into pieces about 1-1/2 inches square. Allow to marinate at room temperature at least 15 minutes and up to an hour.
Meanwhile, combine cornstarch, flour, salt in a shallow bowl.
Drain marinate from chicken (it’s okay if bits of garlic and ginger stick) and coat each piece in the flour mixture. Transfer to a plate and let sit for 10 minutes.
Heat 1/2 inch of oil to 350ºF and fry the chicken in two batches, about 6 minutes each.