Mise en place - Finely mince the ginger. You don't need to peel it, but you should trim away any dry bits. Peel and mince the garlic. Trim and thinly slice the scallions, white and green parts, and set aside.
Simmer - Pour in the chicken broth and tamari, and bring the mixture to a boil, then reduce the heat to a simmer. Stir in the rice vinegar, and miso paste.
Finish and Serve - Turn off the heat. Stir in a handful of fresh spinach until just wilted, then add a tablespoon of toasted sesame oil and the green parts of the scallions.