Boil water in a large pot and add chow mein egg noodles, soaking them for 30 seconds to 1 minute until just softened. Drain the noodles in a colander and set aside.

In a mixing bowl, combine dark soy sauce, regular soy sauce, oyster sauce, fish sauce, granulated sugar, and water. Stir the mixture well until the sugar is fully dissolved.

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

Return the wok to the heat, adding another tablespoon of corn oil. Once hot, add the prepared chow mein noodles and pan-fry for approximately 2 minutes until golden and crispy, then flip for another 2 minutes.

Add the sautéed onion mixture, green onion tops, and bean sprouts to the wok. Pour the prepared sauce over and mix gently, cooking for 1-2 minutes until well-coated.

Drizzle the sesame oil over the noodles, stirring to incorporate the flavor. Serve immediately, garnishing with remaining green onion tops.