1.Cook rice according to packet directions until tender. Cover to keep warm.
2.Meanwhile, shell and devein prawns, leaving tails intact.
3.Heat oil in a wok over high heat; stir-fry onion, garlic and ginger for 3 minutes or until onion is soft. Add seeds, cumin, coriander, chilli and curry leaves; cook, stirring, until seeds pop.
4.Add combined coconut cream and the water. Bring to the boil, then simmer, uncovered, for 5 minutes or until sauce thickens. Add prawns and choy sum; simmer, uncovered, for 5 minutes or until prawns change colour and are just cooked.
5.Serve prawns with rice; sprinkle with coriander.
To save time, buy shelled prawns with the tails intact from the frozen section of supermarkets; defrost in the fridge before cooking. Serve with steamed asian greens, if you like.