Thai minced chicken salad

Name: Thai minced chicken salad
Ingredients: 2 lemongrass; 4 lime leaves, stalks removed; 2 red chillies, deseeded; 3 garlic cloves; fingertip-length piece fresh root ginger; 4 skinless chicken breasts; 1 tbsp vegetable oil; 1 tbsp sesame oil; 1 tsp chilli powder; 50ml fish sauce; 1 red onion, chopped; 3 tbsp lime juice; handful each mint, basil and coriander leaves, roughly chopped; 3 Baby Gem lettuces, leaves separated; 1 cucumber, seeds removed and cut into strips lengthways; 200g beansprouts; lime wedges, to serve