Slice the pork tenderloin into 1/4-inch-thick pieces. In a bowl, combine the marinade ingredients: the dark soy sauce, sherry, and cornstarch. Add the pork and mix; let stand for at least 10 minutes.
In a carbon-steel wok, heat the vegetable oil over high heat until just smoking. Add the scallions and ginger, and stir-fry until aromatic, about 30 seconds. Add the pork, reserving any remaining marinade, and stir-fry for about 5 minutes, until the pork is just done.
Add the green and red peppers, and stir-fry for another minute. Add the hoisin sauce, sherry, salt, and black pepper, and combine. Add 2 tablespoons of water to the marinade remaining in the bowl and add to the wok. Toss to blend well.
Remove from the heat, drizzle with the sesame oil, and serve immediately.