Heat remaining 1 tablespoon oil in a medium saucepan over medium-high. Add garlic and ginger and cook, stirring often, until garlic is golden brown, about 2 minutes. Add chiles, soy sauce, sugar, vinegar, and 1/2 cup water and bring to a boil; stir in cornstarch slurry. Simmer, stirring, until sauce coats spoon, about 2 minutes. Let cool slightly.