In a medium saucepan, bring 4 cups of water to a gentle simmer over medium heat.
Add the dried wakame seaweed to the water and simmer for 2 minutes until rehydrated.
Remove approximately 1/2 cup of the hot water and place it in a small bowl with the miso paste.
Whisk the miso paste and hot water together until a smooth, lump-free slurry is formed.
Reduce the saucepan heat to low to ensure the water does not boil, as boiling can degrade the miso flavor and probiotics.
Stir the miso slurry and the soy sauce into the saucepan.
Add the cubed tofu and simmer gently for 2 minutes until the tofu is heated through.
Turn off the heat and stir in the sliced green onions.
Serve immediately in warm bowls.