Trim the water spinach, including both leaves and stems, into bite-sized pieces about 3 inches long (you can separate the leaves for soup and stir-fry the stems if you prefer). After trimming, soak in salted water for about 5 minutes, then rinse thoroughly and drain.

Heat a pan, add oil, and when the oil is hot, add the garlic and sauté until fragrant and golden. Add the water spinach and stir quickly over high heat for about 30 seconds. Add 1/2 tablespoon sugar, 1 1/2 tablespoons oyster sauce, and 1 1/2 teaspoons seasoning powder, then stir quickly for another 30 seconds.