In a bowl, combine all the sauce ingredients. Set aside.
In a large bowl, dredge the tofu in the cornstarch. Shake to remove any excess and set aside on a plate.
In a wok over high heat, heat the oil. Fry half of the tofu at a time until lightly browned. Season with salt and pepper. Using a slotted spoon, remove the tofu from the wok and drain on paper towels.
In the same wok, fry the onions, ginger and garlic for 1 to 2 minutes. Add oil, if needed.
Add the sauce and bring to a boil. Add the tofu and cook, stirring to warm through, and coat thoroughly with the sauce. Serve with rice and broccoli.