Take mushrooms, salt, pepper, cornflour, all purpose flour, soy sauce in a bowl and mix well. Add little water if needed.
Heat 2 tblsp of oil in a nonstick pan, add mushroom and saute till golden. Remove and set aside.
Heat 1 tblsp oil in a pan. Add onions, chillies and garlic. Saute for a min.
Add in capsicum and mix well.
Add in soy sauce, sugar, salt, vinegar and mix well.
Add chilli flakes and water.
Add mushroom back in and bring it to a boil.
Add the remaining cornflour mixture and mix well.
Add in spring onions and mix well.
Serve