Cut tofu, zucchini, and onion into bite-sized pieces.
Bring 400ml of water and 1 piece of kelp to a boil in a pot.
When it starts to boil, remove the kelp and dissolve 20g of soybean paste in the water.
Add the prepared vegetables and simmer over medium heat for 5 minutes.
Add the tofu and cook for another 3 minutes.
Add green onions, bring to a boil once more, and finish.