In a bowl, mix together the water, soy sauce, sugar, gochugaru, minced garlic, and a pinch of black pepper to create the base sauce.
Slice the tofu and arrange it in a pan, then chop the onion and add it to the sauce mixture.
If desired, include some sliced chili peppers for extra heat.
Bring the mixture to a boil and let it cook for 10 minutes.
At the end of cooking, drizzle sesame oil over the tofu and finish by sprinkling sesame seeds on top.
