Prepare the chicken by patting pieces dry. This helps the coating crisp up nicely.
In a wide bowl, whisk together 1 cup flour, 2 tbsp cornstarch, white pepper, and salt. Toss the chicken pieces in the dry mixture until evenly coated.
Heat oil in a deep skillet or wok to about 350°F (175°C). Fry the coated chicken in batches until golden and crisp, about 3–4 minutes per batch. Remove with a slotted spoon and drain on paper towels.
In a separate pan, combine 2 tbsp soy sauce, rice vinegar, hoisin sauce, oyster sauce, five-spice, garlic powder, and ginger powder. Bring to a gentle simmer.
Make a slurry by whisking 1 tbsp cornstarch with 2 tbsp water; stir into the sauce to thicken. Add minced garlic and grated ginger, simmer for another 1–2 minutes.
Stir in sesame oil, brown sugar, 3 tbsp rice vinegar, 2 tbsp soy sauce, and optional sriracha. Simmer until the glaze is glossy and coats the back of a spoon, about 2–3 minutes.
Toss the fried chicken in the sauce until evenly coated. Serve immediately with steamed rice and your favorite greens.