1. In a small bowl, combine the stock, soy sauce, mustard, vinegar, sesame oil and chili oil.
2. In a large pot of boiling water, blanch the carrot for 1 minute. Using a slotted spoon, transfer the carrot to a plate. Add the noodles to the pot and cook, stirring, until they are al dente, about 5 minutes. Drain the noodles and return them to the pot. Fill the pot with cold water and swish the noodles to cool them. Drain and repeat. Transfer the cooled noodles to a colander and lift them occasionally with your fingers to help dry them out.
3. Meanwhile, in a large, deep skillet, heat the vegetable oil until shimmering. Add the pork slices in a single layer, season with salt and pepper and cook over high heat, without stirring, until browned on the bottom, about 2 minutes. Stir a few times, then add the ginger and stir-fry over moderately high heat until fragrant, about 2 minutes. Add the bell pepper and carrot and stir-fry for 1 minute. Add the noodles to the skillet and toss until well combined. Add the soy sauce mixture, shiso, scallions and bean sprouts and toss until heated through. Transfer to a large, shallow bowl and serve.