In a large skillet, heat 1 tablespoon of the vegetable oil. Add the pork, season with salt and pepper and stir-fry over high heat until cooked, 2 minutes. Transfer to a plate. Add the remaining vegetable oil to the skillet. Add the garlic and crushed pepper and stir-fry for 1 minute. Add the leek and 1/4 cup of the stock, cover and cook until the leek is softened, 2 minutes. Add the remaining 3/4 cup of stock and bring to a simmer. Add the tofu, then stir in the pork, hoisin, vinegar and sesame oil. Transfer to bowls and serve.