Cook the noodles according to package instructions. Drain and set aside.
Heat the sesame oil in a small pot over medium heat until fragrant, about 3 to 4 minutes.
Add the chili flakes, garlic, ginger, three-quarters of the green onions, and sesame seeds to a heatproof bowl. Carefully pour the hot oil over the mixture.
Stir in the nut butter, soy sauce, and lime juice until smooth.
Add the cooked noodles and toss well to coat.
Garnish with the remaining green onions and extra sesame seeds. Serve immediately.
Notes
Adjust the chili flakes to control the heat level.
Any nut butter works, but peanut butter adds the richest flavor.
If your noodles feel dry, add a splash of noodle cooking water to loosen the sauce.