Using a sharp knife, cut the pork into thin slices. Whisk 2 tablespoons of the soy sauce, the cornstarch, salt and white pepper together in a medium bowl. Add the pork and mix well.
Cut the cucumbers crosswise in three pieces. Using the flat side of a large, heavy knife, lightly crush the cucumber pieces, then tear them into chunks; discard any loose seeds.
Heat the canola oil in a very large cast-iron skillet or wok over high heat until nearly smoking. Add the pork and spread it in an even layer. Cook, undisturbed, until well browned on the bottom, about 3 minutes. Add the ginger and garlic and stir-fry until very fragrant and the pork is nearly cooked through, about 3 minutes. Add the cucumbers and stir-fry until the cucumbers are hot, about 3 minutes longer. Stir in the scallions and the remaining 1 tablespoon of soy sauce; season with salt and white pepper to taste. Serve right away with rice and sambal oelek.