Soak the brown rice in 500ml water for 2 hours. Drain and set aside.
Marinate the prawns in the lemon juice and salt.
Set aside 1 tablespoon each of the coriander and grated fresh coconut for the garnish. Grind the remaining coriander and coconut with the green chillies, ginger, garlic and mint to a fine paste.
Heat the oil in a thick-bottomed handi and add the cinnamon stick, cardamom, star anise, cloves and cumin seeds. Sauté for 1 minute.
Add the chopped onion and sauté for 3–4 minutes, or until it turns light golden brown in colour. Add the masala paste and stir-fry for a further 30 seconds.
Add the soaked rice and stir gently for 1 minute. Stir in the coconut milk and 1 litre water. Bring to the boil, stirring once or twice, then cook on a medium heat until the water has almost disappeared – about 30–35 minutes.
Add the prawns, reduce the heat and cook, covered, until the rice is tender.
Remove the pan from the heat and serve garnished with the reserved coriander leaves and grated coconut.