Begin by slicing your flank or sirloin steak thinly against the grain. In a mixing bowl, combine baking soda, cornstarch, kosher salt, 2 tablespoons of soy sauce, mirin, and 2 tablespoons of vegetable oil. Coat the beef slices in this mixture and marinate for at least 1 hour.

Prepare the sauce by mixing oyster sauce, hoisin sauce, remaining soy sauce, and brown sugar in a separate bowl until the sugar dissolves.

Heat 1/4 cup of vegetable oil in a large wok over medium-high heat. Add the marinated beef in batches, stir-frying until caramelized, then transfer to a plate.

In the same wok, add minced garlic, ginger, green onion whites, and dried red chilies. Stir-fry for 30 seconds until fragrant.

Pour the sauce into the wok and bring it to a simmer. Add the sautéed beef and reserved green onion tops, stirring to coat evenly.

Allow to simmer for about 5 minutes, stirring occasionally until the sauce thickens and the flavors meld.