1Heat a large skillet or wok over medium-high heat.
Add the sliced onion and serrano pepper to the skillet and stir-fry for 2-3 minutes until they start to soften.
Add the shredded cabbage to the skillet and continue to stir-fry for another 5-7 minutes until the cabbage is tender but still slightly crisp.
Stir in the chili garlic sauce, sugar, salt, and black pepper. Mix well to ensure the cabbage is evenly coated with the sauce.
Cook for an additional 2-3 minutes, allowing the flavors to meld together.
Remove from heat and serve hot.