Take each chicken breast and bash it gently with a rolling pin to flatten it out to an even thickness (this will help it to cook evenly). Mix the lemongrass paste and soy sauce together in a shallow dish, add the chicken and turn to coat, then set aside to marinate.
Put the noodles into a heatproof bowl and pour on enough boiling water to cover them. Leave to soften for 10 minutes.
Meanwhile, mix the ingredients together for the dressing.
When the noodles are softened, drain and run cold water over them to cool. Drain again and place in a bowl with the carrot, cucumber and mangetout. Add the dressing and toss to mix well.
Place a chargrill pan over a medium-high heat. Drizzle the oil over the chicken fillets and lay them in the pan. Cook for 2-3 minutes on each side. Remove to a warm plate and leave to rest for a minute.
Divide the noodle salad between serving bowls. Slice the chicken and place on top of the noodles. Sprinkle with some chilli slices, chopped peanuts and coriander and serve, with lime wedges on the side.