1If using udon noodles; cover with cold water for 20 minutes, drain. Meanwhile, fill a large sauce pot 3/4 full with salted water; bring to a boil. Add noodles; cook until firm-tender, about 2 minutes. Drain and rinse under cold water; set aside in a large serving bowl; covered.
2If using spaghetti cook in salted water according to package directions; drain and rinse under cold water; set aside in a large serving bowl.
3In a large skillet heat 1 tablespoon of oil until hot. Add pork; cook, stirring frequently, until no longer pink, about 3 minutes; cool slightly. Add to pasta along with bok choy, mushrooms and red peppers. Toss with Spicy Peanut Sauce. Serve garnished with enoki or white mushrooms cut in strips, and chopped salted peanuts, if desired.
4Spicy Peanut Sauce:
In a small bowl combine peanut butter, ketchup, vinegar, water, soy sauce, ginger, sugar, garlic and red pepper.