Mix the chicken thighs with the fish sauce and sugar; let sit while you prep other ingredients.

If using large chili flakes or whole chilies, blitz them in a coffee grinder to turn them into finer flakes.

Make the sauce by combining the oyster sauce, Golden Mountain sauce, water, and sugar, and stir to dissolve the sugar.

Heat the wok over high heat until very hot, then add just enough oil to coat the bottom. Add the chicken and spread it out into one layer and let it sear for about 2 minutes until the underside is brown. Give the chicken a flip so most pieces are turned over (don't worry about every piece), and let them cook on the other side for another 2 minutes, stirring occasionally, until the chicken is fully cooked.

Remove the chicken from the pan, leaving all of the oil and juices behind.

In the same wok, with the heat still off, add the garlic. Turn the heat on medium and saute the garlic until they start to turn golden. Add the chili flakes and stir for about 30 seconds until the chilies smell toasty and are darkened slightly, adding more oil if it looks dry.

Once the chilies are toasted, immediately add the sauce (do this quickly as the chilies burn fast) and stir to mix. Let the sauce simmer for 15-30 seconds until it is reduced slightly.

Add the chicken back in, along with all the collected juices, and toss the chicken in the sauce until all the pieces are coated. If there's a lot of sauce pooling, keep cooking to dry it out a bit. There will be some oil pooling, but most of the sauce should be reduced enough to coat the chicken pieces.

Prepare the green onions: For the green onions, cut the green parts into 2 inch pieces and split the white parts and cut it into thin strips. Discard the roots.

Make the scallion oil (makes 4 servings): First prepare the sauce. Combine both of the soy sauce and sugar. Stir to combine and set aside.

In a sauce pan, add the oil and heat it until it's around 235°F/113°C. You can also test using a wood chopstick or wood spoon. If there's a constant stream of small bubbles, the oil is hot enough.

Once the oil is hot, turn the heat to medium low and add the green onions, both the white and green parts. Gently stir and let it slowly fry until they are golden, about 5 minutes. Then remove the green onions and let them drain on some paper towels.

After removing the green onions, add the prepared sauce mixture to the scallion oil. Bring it to a simmer over medium low heat and let it cook for 1-2 minutes.

Assemble: Bring a pot of water to a boil and cook the wheat noodles till al dente. Portion the noodles and top each serving with 2 tablespoons of the scallion oil noodle sauce. Make sure to stir up the sauce before use to get an even amount of oil and sauce.

Top the noodles with the Chili Garlic Chicken, garnish with the fried scallions and mix well. Enjoy while hot!