Prepare the noodles according to the packet instructions, rinse with cold water, drain and set aside. Bring the water to the boil in a large pan, add the miso paste, tamari, sugar, mushrooms and spring onions, simmer for approx. 5 mins. Add the spinach, simmer for a further 30 seconds. Divide the noodles between two dishes, pour the hot soup over the top, serve immediately.