Serve these spicy lo mein-style noodles as a main-dish or side dish. For a totally vegetarian recipe, replace the chicken broth with vegetable broth.
Cook linguine in a large pot of lightly salted water following package directions. Drain, and immediately plunge into an ice water bath. Set aside.
Meanwhile, in medium-size saucepan, combine peanut butter, chicken broth and water, rice vinegar, soy sauce, sugar, sesame oil, ginger, garlic powder and red pepper flakes. Whisk until combined. Cook on medium-high heat for about 10 minutes or until thickened. Remove from heat.
While sauce simmers, toast sesame seeds in a nonstick skillet over medium heat for 5 minutes, shaking pan to keep seeds from burning.
Drain noodles, discarding ice cubes. Toss with half of the dressing (about 3/4 cup), and allow to soak in for a few minutes. Add remaining dressing and toasted sesame seeds to noodles and toss until well combined. Top with sliced scallions and serve cold. Best if served on the day it is made.