Put the oil in a frying pan or wok (kadhai). Heat it over medium flame.
When it is hot, add the mustard, cumin and sesame seeds. When they begin to pop, add the hing, turmeric powder, ginger and chilli paste. Saute for a few seconds.
Add the cauliflower and potatoes. Mix well. Add the salt, mix and cover the pan.
Cook on low flame till the vegetables are just done and not over cooked. It usually takes about 5 to 7 minutes to cook.
Switch off the heat. Add the sugar, coriander cumin powder and lemon juice. Mix well.
Add the fresh coriander just before serving.