Leave 2 tbsp oil in the same pan after removing the excess oil from it and fry the onions on high heat till translucent.
Add the garlic, and fry for a further 30 secs.
Add water or chicken stock and cook till it gives a boil.
Add soy sauce, red chilli sauce, tomato sauce. Mix well and let the sauce simmer for a couple of minutes.
Add the cornflour paste to thicken the sauce while stirring continuously.
Add vinegar and the fried chicken pieces. Let it simmer till it reaches your desired consistency.
Serve the chicken manchurian gravy hot garnished with spring onion.