Cut the tofu and mushrooms into bite-sized pieces.
Slice the onion and green onion.
Heat cooking oil in a pan and grill the tofu until golden brown.
Push the tofu to one side and sauté the mushrooms and onions.
Mix soy sauce, sugar, minced garlic, and water to make the sauce.
Pour the sauce over all the ingredients and simmer over medium heat.
Add the green onion, simmer once more, then serve on a plate.