Heat 2 tablespoons of oil in a wok, stir-fry the prawns for 1-2 minutes, season with cayenne pepper and salt and remove with a slotted spoon. Pour the remaining oil into the wok and fry the asparagus for 3 minutes while turning. Add ginger, garlic, peppers and spring onions and fry briefly. Mix the cornstarch with the lobster stock, stir into the vegetables, pour in the coconut milk, bring to the boil and simmer over a medium heat for 4 minutes.
Stir in the prawns, season with cayenne pepper and a little salt. Finally stir in the coriander leaves.