Thinly slice the flank steak against the grain into 2 ½ inch (6 cm) pieces, and add to a medium bowl along with 1 ½ tablespoons water, the cornstarch, oil, oyster sauce, and baking soda (if using). Set aside for 20-30 minutes while you prepare the other ingredients.
Slice the tofu into ½ inch to ¼ inch (about 1 cm) thick rectangles, and set aside.
In a small bowl, make the sauce mixture by combining the hot water, sugar, hoisin sauce, dark soy sauce, light soy sauce, sesame oil, and white pepper. Mix well until the sugar is dissolved.
Prepare the bell pepper, ginger, garlic and scallions. Slice any thicker pieces of scallion in half lengthwise.
Heat the wok over high heat until it just begins to smoke. Only when it’s begun to smoke, add 1 tablespoon of oil to coat. Carefully lay the slices of tofu in the wok in a single layer, and sear for about 2 minutes per side or until golden brown. Set aside on a plate.
Again, heat the wok over high heat until smoking and add another tablespoon of oil. Add the beef in a single layer, and sear for 30 seconds to 1 minute. Stir-fry for another 15-30 seconds, until the beef is about 75-80% cooked. Remove from the wok, and set aside.
Add another ½ tablespoon of oil to the wok, along with the ginger slices. Caramelize and brown them for about 20 seconds. This infuses the oil and wok with all that ginger flavor. Add the garlic, white portion of the scallions, and red pepper, making sure the heat is still on high. Stir-fry for about 10 seconds, and add the Shaoxing wine.
Continue to stir-fry for another 30 seconds, and add the pan-fried tofu, beef (along with any juices), and sauce mixture. Stir-fry for another 20 seconds, until the sauce coats all the ingredients.
Add the green parts of the scallions, and stir-fry until the scallions are wilted. Plate and serve immediately with steamed rice.