Heat 1 tablespoon of water in a large pot or Dutch oven over medium heat. Add the minced ginger with a pinch of salt, and saute about 1 minute, or until ginger becomes fragrant.
Add the hot broth, increase the heat to high to bring to a boil, then reduce heat to medium low and simmer 5 minutes. (Simmer longer if you want a more intense ginger flavor. If using chopped frozen spinach, add it now.)
If using fresh spinach, while the broth and ginger are simmering, place the spinach leaves and 1 tablespoon of water in a microwave safe dish, cover, and cook on high for 2 minutes. Then simply cut the spinach with a fork and butter knife. Remove any stems, if desired, then add it to the soup.
Optional: To thicken the soup, while the spinach is cooking, ladle about a cup of broth 2 teaspoons of cornstarch into a bowl, and whisk completely until there are no lumps. Add the mixture back to the pot.
• If you don't want to bother to peel and mince the fresh ginger, cut it into thin slices and simmer in the broth a few minutes longer. Then remove the slices out with a slotted spoon before adding the spinach, or just avoid eating them.