Begin by boiling a pot of water and soaking the Chow Mein egg noodles for 30 seconds to 1 minute until they soften. Stir gently to ensure even cooking, then drain the noodles and set aside.

In a mixing bowl, combine dark soy sauce, regular soy sauce, oyster sauce, fish sauce, granulated sugar, and water. Whisk until the sugar fully dissolves and the mixture is smooth.

Heat 1 tablespoon of corn oil in a wok over medium-high heat. Add the chopped yellow onion and the white parts of the green onions, sautéing for about 1 minute.

In the same wok, add another tablespoon of oil and increase the heat to high. Carefully add the soaked noodles, spreading them in a thin layer. Fry for about 2 minutes on each side until golden brown.

Once your noodles are crispy, stir in the sautéed onions, the green parts of the green onions, and the bean sprouts. Pour the prepared sauce over the mixture and toss everything together.

Remove the wok from heat, and drizzle the sesame oil over the chow mein, giving it one last toss to incorporate the nutty flavor. Serve immediately while it's still hot and crispy.