This is a really quick and easy meal - big reward for little effort.
Cut the prawns along the topside and de-vein. Dust the prawns in the cornflour. Leave to stand for 15 mins.
Make the sauce - put the peppercorns in a small frying pan over a medium heat. Cook, shaking the pan frequently, for 2-3 mins until toasted. Grind coarsley in a pestle and mortar. Stir in the rice vinegar, hoisin and soy and dried chillies.
Heat a wok over a high heat until very hot. Pour in the oil, swirling to coat the sides. Add the prawns and stir fry until they turn pink, about 1- 2 mins. Stir in the sauce and heat through. Toss in the peanuts and serve sprinkled with the sliced chilli and spring onion.