Cut the tomatoes into quarters and boil in 3 cups of water till soft. Mash well and strain through a soup sieve to make purée. Add enough water to this to get a thin soup consistency. Put back on the stove and bring to a boil.
While the tomato purée is boiling, heat the oil in a small pan on a medium flame Add the mustard, fenugreek and cumin seeds, green chillies and curry leaves to the oil and fry till the spluttering stops.
Immediately add this mix to the tomato purée and mix well. Add the red chilli powder, salt and the mixed vegetables and stir. Simmer and cook till vegetables are done.
Garnish with chopped coriander leaves and serve with hot plain boiled rice.