Cut the tofu and mushrooms into bite-sized pieces.
Finely chop the onion, green onion, and garlic.
Heat cooking oil in a pan and sauté the garlic and green onion.
Add the onion and mushrooms, and stir-fry them.
Add the tofu and stir-fry for a little longer.
Pour in soy sauce, red pepper powder, sugar, and water, then bring to a boil.
Simmer until the sauce thickens slightly.
Finish by drizzling sesame oil and sprinkling sesame seeds on top.