1.Rinse rice in a sieve under cold running water until water runs clear. Place 2 cups (500ml) water in a medium saucepan; bring to the boil. Add rice; return to the boil. Reduce heat to low; cook, covered, for 10 minutes. Remove from heat; stand, covered, for 10 minutes. Spread rice out on an oven tray. Refrigerate for 2 hours or until cold.
2.Twist or cut behind the prawn head to remove it. Peel away the shell starting from legs, leaving the tail intact. To devein, make a small cut in the centre back of prawns. Insert a skewer or toothpick through the skin and under the vein, then lift; this will pull the vein out in one piece. Alternatively, run a small knife down the back of the prawn to expose the vein and pull it out that way.
3.Trim green beans; chop finely. Wash coriander paying attention to the roots. Pick leaves from coriander; you will need 1 cup. Coarsely chop coriander stems and roots; you will need ½ cup.
4.Place tom yum paste and chopped coriander stem and root mixture in a large wok over high heat; stir-fry for 3 minutes or until fragrant.
5.Add prawns; stir-fry for 2 minutes or until prawns start to change colour. Add beans and cold rice; stir-fry for 3 minutes or until rice is heated through and beans are tender.
6.Stir half the reserved coriander leaves through rice; serve topped with remaining leaves.
If you have the option, buy coriander sold in bunches rather than pre-packaged, otherwise the quantity will be smaller (and it may not have roots), in which case you may need to buy two packs. The root is the most flavoursome part, and is traditionally used in curry pastes.
Brands of tom yum paste vary in their heat intensity; start adding less and gradually add more to suit your heat level. You can use red thai curry paste instead, if you like.
Want more greens? Stir-fry finely shredded leaves of 1 bunch of gai lan (chinese broccoli) with the prawns.