In a roomy liquid measuring cup or small bowl, stir together 4 tablespoons soy sauce, rice vinegar, hoisin, peanut butter, ginger, and garlic. Keep near the stove.
In a large, deep skillet or wok, heat 1 tablespoon of the oil over medium-high to high heat. Once the oil is hot and shimmering, add the pork. Cook 3 minutes on all sides, then add 1 tablespoon of the soy sauce and stir to combine. Continue cooking until the pork is browned on all sides and cooked through, about 2 minutes more. Transfer to a large bowl or plate.
Meanwhile, bring a large pot of salted water to a boil and cook the noodles until al dente, according to package directions. Reserve 1 cup of the pasta cooking liquid, then drain and set aside.
Return the now-empty skillet to the stove over medium-high heat. Add the remaining 1 tablespoon oil. Add the stir fry vegetables and edamame, and cook until hot and slightly crisp, about 7 minutes (note that frozen vegetables won’t be crisp-tender the way fresh ones are but they will still be yummy). Remove to the same bowl with the pork.
Reduce the skillet heat to medium and add the soy sauce mixture. Whisk and cook for 1 minute. Add the cooked noodles, reserved pork and vegetables, green onions, peanuts, cilantro, and red pepper flakes (if using). With tongs, toss to combine and evenly coat all of the ingredients. If the mixture seems too thick, add a little bit of reserved pasta water as needed to loosen it. Season to taste. Serve topped with additional chopped peanuts and fresh cilantro.
Notes
TO STORE: Leftover pork stir fry may be kept in the refrigerator for up to 5 days.
TO FREEZE: Pork stir fry may be stored in the freezer for up to 3 months. Thaw overnight in the fridge before reheating. Note freezing stir fry is often an experiment depending on the vegetables used. For best results, stick with firm, crisp veggies if you plan to freeze as opposed to vegetables with a high water content (e.g. zucchini or cabbage).
TO REHEAT: Warm leftover pork stir fry in a wok or skillet over medium heat until heated through. Alternatively, you may also microwave, in a microwave-safe container, until steaming.
SLOW COOKER: Place the pork tenderloin in the bottom of a 4-to-6-quart slow cooker with the sauce mixture. Cover and cook on LOW for 2 to 3 hours (pork tenderloin tends to quick quickly because it is lean so do not overcook), until cooked through. Remove the pork to a large plate, reserving the cooking liquid. Let rest for 10 minutes, then shred with two forks or your fingers. Finish the recipe as directed (starting in step 3), using the reserved cooking liquid from the slow cooker as your sauce in step 5.