Heat the oil in a wok, or large skillet, over high heat until a bead of water sizzles and evaporates on contact. Add 1 tablespoon of the oil and swirl the pan to coat the base and sides. Add the eggplant and stir-fry until outsides become golden brown and insides begin to soften, about 2 to 3 minutes. Add the garlic, ginger, and Sichuan peppercorn and stir-fry until fragrant, about 30 seconds. Pour in the sauce mixture and mix well. Simmer for 3 to 4 minutes to allow the eggplant to full cook and the sauce to thicken enough to coat the back of a spoon. Remove from the heat, plate, and sprinkle scallions on top.