How to Make It
Combine the first four ingredients (through serrano) in a large bowl. Warm grapeseed oil in a small saucepan over medium-high heat until bubbling, but not smoking. Pour hot oil mixture over ginger-scallion mixture and stir. (It’s okay if scallions sizzle.)
Whisk together soy sauce, rice vinegar, sesame oil, salt, and pepper in a small bowl; stir into ginger-scallion mixture. Let stand for at least 15 minutes so the flavors can develop.
Meanwhile, cook noodles according to package instructions (omitting any included flavoring packets). Drain and pour ginger-scallion mixture over noodles and toss until completely coated. Squeeze juice of one lime over noodles. Divide into four bowls and top evenly with sesame seeds.