Wash the water spinach in several changes of cold water, trim the tough stem ends, and cut into 3-inch lengths. Drain thoroughly. Mince the garlic and slice the chiles so everything is ready before the wok heats up.

Heat a wok or large skillet over high heat until it just begins to smoke. Add the oil and swirl to coat.

Add the garlic, chiles, and belacan. Stir-fry about 20 seconds, mashing the shrimp paste into the oil, until pungent and toasty.

Add the water spinach stems first and toss 30 seconds, then add the leaves all at once.

Pour the oyster sauce around the edge of the wok so it sizzles, add the sugar, and toss continuously 60 to 90 seconds, until the leaves are wilted and glossy but the stems still have bite. Add a tablespoon of water only if the pan looks dry.

Taste and add salt if needed. Serve immediately with lime wedges, while the stems are still crisp.