Heat the oil in a wok over a low heat. Add the curry paste and stir-fry for 4 minutes, until the paste is fragrant. Stir the measurement water into the curry paste, bring to the boil and cook over a high heat for 2 minutes to reduce the paste.
Stir the coconut milk into the curry paste, then add the prawns. Cook the curry over a medium heat, stirring occasionally, for about 6 minutes or until the prawns turn pink and are cooked through.
Stir in the fish sauce and lime juice, and season to taste with salt and pepper. Transfer to a warm serving plate. Garnish with the sliced chillies and coriander, and serve with rice, if liked.