Combine all the ingredients of the batter. Dip the chicken pieces in egg batter. Heat oil for deep frying in a pan (refer notes). Once the oil is hot, reduce heat. Add chicken pieces to the oil and increase the heat to low-medium. Fry the chicken pieces till they turn light golden colour. Make sure you dont fry it too long, otherwise the chicken will harden. Keep it aside.
In a wok, heat oil. Lightly fry the crushed ginger and garlic. Add green chillies and white of spring onions. Stir for a few seconds. Add chicken stock/water. Add all the other ingredients of the sauce except cornflour. Cook for 2-3 minutes.
Add 3 tbsp water to cornflour and make a thick paste. Add cornflour paste to the sauce and give one boil. Add fried chicken pieces and cook for 2-3 mins, till sauce turns slightly thick. Serve hot garnished with spring onion greens.