Thai green chicken curry

Ingredients to serve 4:
1 tbsp peanut oil or similar
75g green thai curry paste
3 long green chillies, finely chopped
1kg chicken thigh fillets, cut into 1.5" pieces
2x400ml cans coconut milk (can also be made by soaking dessicated coconut in water then passing through a sieve)
2 tbsp fish sauce
zest and juice of one lime or 2 tbsp lime juice
1-2 stalks lemongrass - I think you're supposed to bash the ends
1 tbsp sugar
75g frozen peas
1 aubergine, diced quite finely - optional
1 large courgette, thinly sliced
fresh basil leaves
fresh coriander leaves
2 spring onions coarsely chopped

1. Heat oil in a large saucepan. Cook the paste and two thirds of the chilli, stirring continuously, for 2 minutes. Add the chicken and lime zest and cook until browned, stirring continuously.
2. Add the coconut milk, fish sauce, lime juice, sugar and aubergine if using. Simmer for 10 mins until aubergine is just tender.
3. Add courgettes, peas and herbs. Simmer until courgettes are tender.
4. Serve sprinkled with with rest of the chilli and the spring onion.