Finely chop the onion and green onion.
Slice the mushrooms thinly.
Heat olive oil in a pan and sauté the onion, green onion, and mushrooms.
Add tomato sauce and bring to a boil.
Add soft tofu and gently stir while simmering.
Top with mozzarella cheese, cover, and cook until the cheese melts.
Transfer to a gratin dish and sprinkle with parsley.