Drain the noodles and add them to the coconut liquid. Chop the chicken from the bone and stir into the soup with the green part of the spring onion. Season with salt and black pepper.
Add half the curry paste (see tip). Stir well to coat the chicken and onions in the paste. Fry for 1–2 minutes, or until fragrant. Add the potato, chillies, stock, coconut milk, tomatoes ...