Cook noodles according to package instructions. Drain and set aside.: The moment you drain the noodles , you will notice their steam and mild wheaty scent, which tells you they are ready to accept the oil based sauce. Rinsing or not rinsing depends on the noodle type, but beware that rinsing removes starch that helps sauce cling. A common mistake is overcooking, which results in limp texture instead of the springy chew you want; aim for just tender with a little bite. If the noodles stick together after draining, toss them with a teaspoon of oil and separate with a fork, keeping them loose so the sauce can coat every strand.
To a large pan, add the oil, green onion, garlic, light soy sauce, rice vinegar, chili flakes, and sugar; whisk to combine.: As the oil warms it will carry the aroma of the chopped green onion and minced garlic throughout the pan, creating an immediate savory scent. Whisking the liquid components together before heating helps the seasonings distribute evenly so each noodle will taste the same. One trap is adding cold liquids to an already burning pan, which can splatter; measure and combine first, then gently warm so the ingredients marry without aggressive sputtering.
Turn on the heat to medium-high and cook for 1 minute or until the garlic is fragrant. Add the cooked noodles to the pan and toss or stir to coat the noodles in the chili oil mixture.: When the pan hits the right warmth you will hear a soft sizzle as the garlic hits the oil and begins to toast, releasing a rich, nutty aroma. That brief cook time is all you need to bloom the chili flakes and remove any rawness from the seasoning. If you see the garlic darkening quickly, lower the heat immediately; burned garlic gives an acrid taste, so it is better to reduce heat than to push for color. Trust your senses, smell is the best indicator here.
Garnish with more green onion or sesame seeds and enjoy immediately.: As you toss, the glossy sheen of the oil will cling to the noodles , and you should see the strands separate and glisten. The sound is subtle, but you may hear light swishing as the sauce distributes. Use tongs or chopsticks to lift and fold so every noodle is coated; unequal coating is a frequent slip that leaves pockets of blandness. If the mixture seems dry, add a teaspoon of hot water to help the sauce emulsify and spread evenly.
Garnish with more green onion or sesame seeds and enjoy immediately.: Immediately after plating, the steam will lift the aroma of the finished bowl and the first bite should carry heat, salt, and a hint of acid in balanced succession. Garnishing adds texture contrast, and the bright green onion will pop against the warm noodles. A common oversight is letting the dish sit, which dulls the vibrant flavors and cools the oil; serve without delay so the textural contrasts remain sharp and the aromatics are at their peak.