In a medium bowl, whisk together the soy sauce, sesame oil, white vinegar, peanut butter, brown sugar, ginger, and garlic until smooth and the sugar is dissolved. Set aside.
Fill a large pot, bowl, or container with ice and half as much water. Cook the noodles until al dente, drain in a colander, and pour the noodles directly into the ice bath, shocking them to stop the cooking. Return to the colander to drain again.
Transfer the noodles to a large bowl, add the sauce, and mix well to combine. If desired, garnish with the chicken, cucumber, cilantro, sesame seeds, scallions, and Everything Spice Crunchy Chili Oil, and enjoy immediately.
Note: Fresh garlic adds a nice kick, but it’s not mandatory. Use the best-quality sesame oil you’ve got and make sure it’s toasted.