Fry the ginger and onion in a dry frying pan over a high heat until deeply coloured. Transfer to the slow cooker and heat to low. Fry the whole spices for a few mins until fragrant, then tip into the slow cooker. If pressed for time, simply put in the slow cooker without frying.
Add the carcass, then pour 3-4 litres boiling water into the cooker so the bones are covered, ensuring you don’t overfill it. Cover and cook for 8-10 hrs, depending on how long you can leave it.
Strain the stock, discarding the bones and spices. Season with the fish sauce and sugar. To freeze for later, leave to cool completely and freeze in an airtight container for up to three months. Keep warm in the slow cooker if serving immediately.
Cook the noodles following pack instructions, drain and divide between bowls. Top with the turkey and beansprouts or veg, then transfer the stock to a jug and pour over enough to fill the bowls (you will have extra, which you can freeze as above). Scatter over the herbs and chilli, then serve with the lime wedges and sauces.