You can assemble this the night before in a Thermos cup and then just pour the boiling water over the top, or put all the ingredients into some Tupperware and pop them into a bowl at work and pour the boiling water over the top. Cut the heads off the shimeji mushrooms and remove the bottom part of the enoki stems. Wash the spinach. Chop the spring onions into small rounds, discarding the stem and the tough green ends. Place all the ingredients except the miso and the water in your container. Remember to take your miso sachet with you to work. When you’re ready to eat, add the miso paste to the other ingredients, pour boiling water over the top and leave for 2-3 minutes, giving it a little stir.