Place water in a large pot, then bring to a rapid boil. Add hondashi powder, crumbled seaweed, and cubed tofu. Stir well. Allow the soup to come back up to a boil, then lower the heat to a simmer and cook.
Turn off the heat. Place miso paste in a fine mesh sieve, then lower that into the soup. Use a spatula or small whisk to help dissolve the miso paste into the water (then remove the strainer).
Finish with thinly sliced green onions, then enjoy warm with a little hot chili oil spooned on top!