Place a wok or large frying pan over medium heat and add the vegetable oil. When the oil is hot, add the garlic and chiles and stir-fry until fragrant, 3 to 4 minutes. Add the pork belly and stir-fry until the fat is translucent, about 3 minutes.
Tilt the wok to pour off all but 1 to 2 tablespoons of the fat. Add the leeks and stir-fry until tender, about 3 minutes.
Add the sugar and stir-fry for 1 minute more. Stir in the soy sauce and serve immediately.
Reprinted with permission from Root-to-Stalk Cooking: The Art of Using the Whole Vegetable, by Tara Duggan, copyright 2013. Published by Ten Speed Press, a division of Random House, Inc.