Heat the oven to 190c.
Cut large rectangles of greaseproof paper and lay down the lemongrass, spring onions, ginger, garlic and some of the basil. Add the coconut oil to each. Season well with a good pinch of salt.
Cook in the oven for 20-25 minutes.
Meanwhile, heat some more coconut oil in a saucepan and sauté the shallots, chilli and garlic for a few minutes until soft. Add the coconut milk and bring to the boil. Add the lime, leaves and fish sauce and reduce to a simmer until reduced a little, just starting to thicken and come together as a sauce rather than a soup. Taste and adjust the seasoning.
Deep-fry the leek shreds briefly until crisp and drain on paper. Sprinkle with salt and chilli powder.
Cook the noodles and serve with the chicken, steamed vegetables, leek and extra basil. If you like, you could serve the chicken in its parcels with the sauce separate and let all the delicious steam escape into the air at the table.