Finely slice the shiitake mushrooms. Marinade in the soy sauce, sugar and sesame oil for 20 minutes.
Meanwhile, make the sauce by mixing together the water, oyster sauce, sugar and sesame oil. Set aside
Pat dry the tofu, dredge in cornflour and set aside.
Heat a large frying pan with 1 tablespoon oil over high heat. Reduce the heat to medium, then fry the tofu until evenly brown on both sides, about 4-5 minutes. Transfer to a serving dish.
In the same frying pan, heat 1 tablespoon oil over high heat. Stir-fry the garlic until aromatic, 2-3 minutes. Stir in the onion and salt, cook until soft, 3-4 minutes. Add the shiitake mushrooms, baby corn, vegetables and scallops to the pan and stir well.
Stir in the sauce and heat through, 1-2 minutes. Pour over the plated tofu and serve.
Dried shiitake mushrooms and dried scallops can be purchased in Chinese/Oriental speciality stores.