Soak wakame in a bowl for 10 minutes. Drain. Place miso in a bowl.
Bring homemade dashi in a medium sized saucepan to a boil. Scoop up about ¾ cup (180ml) boiling dashi and pour it over miso. Mix with a fork until miso dissolves.
Add tofu and wakame to the sauce pan. Bring it back up to a boil.
Pour dissolved miso back into the saucepan. Turn off heat just before soup comes back up to a boil.
Serve in individual bowls sprinkled with sliced green onions.