Heat oven to 180C/160C fan/gas 4. Toss the squash with 1 tbsp oil and some seasoning on a baking tray, arrange in a single layer and roast for 35-40 mins, or until soft and starting to caramelise around the edges. Meanwhile, heat the remaining oil in a deep pan or casserole dish. Season the chicken, then cook until browned all over. Add the garlic and ginger, stirring for a min or 2, then add the stock, coconut milk, whole chillies, soy and 250ml water. Bring to a gentle simmer, cover with a lid and poach the chicken for 20 mins.
Remove the chicken, shred the meat with forks and return to the soup, discarding the bones. Spoon 2-3 tbsp of the soup into a bowl with the peanut butter and mix until smooth. Add to the soup with the juice of 1 lime, the sugar and the fish sauce. Check the seasoning, adding more lime, sugar, soy or fish sauce if you want to. Keep the soup warm while you cook the noodles following pack instructions.
Drain the noodles and add a handful to each bowl. Pour over the soup and top with the squash, spring onions, coriander, beansprouts, peanuts, chilli oil and sliced chilli (if using). Serve with extra lime wedges.