Bring a medium pot of well-salted water to a boil.
Meanwhile, in a large bowl, whisk together the peanut butter, coconut milk, teriyaki sauce, lime juice, fish sauce, chile paste, and 1/3 cup hot water until smooth. Set aside at room temperature.
Boil the pasta according to package directions until tender, drain, and spread out on a baking sheet to cool to just a bit warmer than room temperature.
Add the pasta to the sauce in the bowl and toss. Add the cilantro, cucumber, and scallions, and toss well again.
Enjoy right away or chill to serve cold. Before serving, taste and add salt, if needed, plus additional lime juice or chile paste or Tabasco to taste, as cold can dull flavor.