In a heatproof bowl, combine the chili flakes, minced garlic, sugar, light soy sauce, dark soy sauce, and oyster mushroom sauce. If your sesame seeds are unroasted, add them now. If they’re roasted, they will be added later.
In a small saucepan, heat the neutral oil over medium heat until hot but not smoking. This should take about 2-3 minutes.
Carefully pour the hot oil into the bowl containing the sauce ingredients. Stir immediately and thoroughly to combine. If you have reserved roasted sesame seeds, stir them in now.
Cook the noodles according to the packet's instructions.
In a mixing bowl or in the pot you cooked the noodles in, combine the cooked noodles with the spicy chili garlic oil, and add the sesame oil.
Garnish with freshly chopped cilantro or sliced spring onions.