Boil the colocasia tubers and the potatoes and remove the husk. Cut potatoes into two inch pieces. Leave the smaller colocasia uncut but cut the larger ones into two each.
Cut the brinjals into medium sized pieces and leave them in water.
Take a deep bottomed pan, add oil and heat. Splutter mustard seeds, add onion pieces and fry until brown in color.
Now add the potato, colocasia, brinjal and drumstick pieces. Stir and add red chilly powder, coriander and cumin seed powders. Mix well and fry until the raw smell is gone.
Add water, place a lid on the pan and allow the contents to simmer in medium flame until the vegetables are well cooked.