Heat saucepan on medium-high heat, then add oil and garlic. Cook until it becomes slightly golden, about 30 seconds-1 minute. Add 1 cup of water, sugar, salt, fish sauce, garlic chili sauce, vinegar, and black pepper. Combine well and allow to slowly come to boil. Once mixture comes to a boil, immediately reduce heat to low simmer.
Slowly add the cornstarch/water mixture until it becomes thick enough to allow sauce to cling to wings.
Cook the Wings: Preheat oven to 425° F. Line a baking sheet pan with parchment paper.
On prepared baking sheet pan, spread chicken wings out in one even layer (we don't coat our wings with oil before baking, but you can if you want. We find that the oil just makes the wings greasier. The wings release enough fat already). Season chicken wings with salt and pepper.
Bake for about 45-50 minutes until golden brown, flipping the wings halfway through baking, after the first 25 minutes or so.