Combine water and dashi granules in a medium saucepan over medium-high heat; bring to a boil.
Reduce heat to medium and whisk in miso paste. Stir in tofu. Separate the layers of green onions, and add them to the soup. Simmer gently for 2 to 3 minutes before serving.
Expert Tips
Dashi is a basic stock used in Japanese cooking which is made by boiling dried kelp (seaweed) and dried bonito (fish). Instant dashi granules are sold in conveniently sized jars or packets and vary in strength.