Heat oil in a pan and add mustard seeds. When it crackles, add cumin seeds and hing. Now add finely chopped onion to it and saute it until light pink in colour. Now add spring onion, ginger and garlic paste to it. Cook it for one minute and add turmeric, red chilli powder, cumin-coriander powder, garam masala and salt. Mix everything well and cook it for one or two minutes. Now add finely chopped tomatoes to it and let the tomatoes cook until soft.