Boil noodles in salted water and remove about 30 seconds early. Save pasta water and rinse noodles to prevent them from sticking together.
In a cold pan, combine peanut butter, chili flakes, green onion, sesame seeds, garlic, 1 tablespoon chili crisp, rice vinegar, and dark soy sauce without heat.
Heat ⅓ cup neutral oil until very hot, then carefully pour it over the cold ingredients and stir well.
Add noodles and toss until completely coated and glossy. For extra silkiness, heat on medium-low and add a splash of reserved pasta water.
Remove from heat, top with extra green onion, chili crisp, and a squeeze of lime if desired.
