Cook pasta according to package instructions. While pasta is cooking, rinse and dry bok choy, bean sprouts, and scallions. Quarter bok choy lengthwise and thinly slice scallions. Drain pasta and set aside. In a large sauté pan or wok, heat oil over high heat. When the pan is very hot, add thawed vegetables and bok choy. Stir to combine and continue to cook and stir for 2 to 3 minutes. Add cooked pasta and toss vegetables, stirring continually another 2 to 3 minutes. Add teriyaki sauce. Toss and continue cooking for another 1 to 2 minutes. Remove from heat. Add sprouts and scallions and toss again.