MAKE THE SAUSAGE: In a large bowl, mix together the pork, lemongrass, garlic, ginger, salted shrimp, coriander, fish sauce, and shallot. Using gloved hands - really, hands work best - blend the mixture until very well incorporated. Set aside.
MAKE THE PESTO: In a blender or the bowl of a food processor, whirl together the mustard greens, mint, and cilantro until chopped. Add the mirin, sake, fish sauce, oil, vinegar, caraway, and red pepper flakes, and blend until evenly green, with no large pieces remaining, pausing to scrape down the sides of the bowl if necessary. Transfer the sauce to a small bowl (or 2-cup glass measuring cup with a spout, for easy measuring later).
PREPARE THE NOODLES AND GET READY TO COOK: When you’re ready to cook, trim the rounded ends off the patty of chow fun, then cut into 3/4-inch strips and transfer the noodles to a large bowl, breaking them into long individual strips if you can. (They’ll continue to break apart in the pan. If they seem particularly stuck together, put them in the microwave for about 10 seconds at a time, until they’re soft enough to peel apart, or give them 30 seconds or so in a steamer.) Gather the sausage, Togarashi, pesto, oil, pea vines, peas, and noodles in a spot near the stove. (You’ll be making the noodles in four quick batches, so it’s nice to have everything nearby.)
FRY THE SAUSAGE AND NOODLES: Heat a large skillet or wok over medium-high heat. When hot, working quickly, add about 2 tablespoons of the canola oil to the pan, then scatter a quarter of the sausage over the pan in big bite-size chunks. Let the sausage cook for about 3 minutes, turning once or twice, then add a quarter of the noodles and cook, stirring, for another 2 minutes, until the noodles are soft and the pork is cooked through. Stir the pesto, then add about a 1/2 cup of the pesto, and a quarter of the pea vines and peas, and toss just until combined. Transfer the noodles to Asian-style noodle bowls, sprinkle with Togarashi, and serve immediately. Repeat with the remaining ingredients, wiping out the pan (or using a different pan) when necessary between batches.
MAKE THE TOGARASHI: Dry the orange zest first. Preheat the oven to 300 degrees F. Place the orange zest in a small ovenproof dish and bake for about 15 minutes, or until shriveled and totally dry, stirring once or twice. Set aside to cool completely. Transfer the cooled zest to a small bowl and stir in the sesame seeds, chili flakes, ginger, and garlic powder.