Cut tofu, green onion, and seaweed into bite-sized pieces.
Pour water into a pot and bring to a boil.
Add kelp to the boiling water to make broth.
Remove the kelp once the broth is ready.
Dissolve miso paste into the broth.
Add tofu, seaweed, and green onion, and let it simmer briefly.
Turn off the heat and serve in a bowl.