In a bowl, whisk together light soy sauce, Chinese black vinegar, sugar, and oyster sauce until well combined and glossy.

In a separate bowl, dissolve cornstarch in cold water until smooth.

Heat canola oil in a wok over medium-low heat for 1-2 minutes.

Add minced garlic, dried red chilies, and chopped scallions to the hot oil and sauté for 1 minute.

Raise the heat to high and add the Napa cabbage stems. Stir-fry for 2-3 minutes.

Pour the prepared sauce over the stir-fried cabbage and cook for an additional minute.

Add the cornstarch slurry to the wok, stirring continuously for about 1 minute until the sauce thickens.

Remove from the heat and serve immediately.