Can't find udon noodles? Make this dish with spaghetti—like Rach's mom used to do.
Bring a large pot of water to a boil for the noodles.
Shred enough of the chicken to measure about 2 cups. (Reserve the remaining chicken for another use.)
In a large bowl, microwave the peanut butter on high until softened, about 30 seconds. (Or, in a small saucepan, stir the peanut butter over low heat until softened, then transfer to a large bowl.) Whisk the apple juice, vinegar, soy sauce, honey, oil, and chile sauce into the peanut sauce.
Cook the udon in unsalted water (or the pasta in salted water), according to the package directions. Drain the noodles and run under cold water until cool, then drain well.
Mix the noodles, celery, radishes, scallions, bean sprouts, and chicken into the peanut sauce. Top with the sesame seeds.