Heat the oil in a large frying pan or wok. Add the cumin seeds, curry leaves and onions and cook over a medium low heat for 10 minutes, stirring occasionally, until the onions are golden.
Add the turmeric, chilli powder, tomato puree, tomatoes and a little salt. Cook for 5 minutes, stirring occasionally.
Add the prawns and cook for a further 5-6 minutes or until they turn pink and are cooked through.
Serve scattered with chopped coriander leaves on toasted poppadoms or with parathas.