Boil dried udon in well-salted water according to package until just tender. Drain and rinse under cold water to stop the cooking. Shake off excess water and set aside.
Build the Sauce
In a medium-hot pan, add neutral oil, chili crisp, scallions, garlic, light soy sauce, dark soy sauce, sesame oil, sugar, rice vinegar, and chicken stock. Stir and let it sizzle 20 seconds.
Toss the Noodles
Add udon directly to the pan and toss continuously until every strand is fully coated and glistening. Work quickly so the noodles pick up sauce evenly before it tightens.
Plate and Finish
Twirl noodles into a high mound and spoon any remaining sauce from the pan over the top. Finish with fresh scallion greens, sesame seeds, and a heavy chili crisp drizzle.