In a serving bowl, combine the MSG, chili oil, yacai, sugar, soy sauce, and green onions. Stir until the MSG is fully dissolved.
Boil the noodles until just past al dente. Drain quickly, give them a brief shake, then immediately toss with the sauce until evenly coated.
Notes
Drain the noodles in just a couple of quick shakes—don’t leave them exposed to air for more than a few seconds. If they clump or seem hard to toss, loosen them with a small splash of hot water.