Preheat your oven to 325°F (165°C). Lightly grease a 9x13-inch baking dish.
Place cornstarch in a shallow bowl and the beaten eggs in another. Dredge each chicken piece in cornstarch, then dip in the egg.
Heat oil in a skillet over medium-high heat. Quickly brown the chicken in batches, about 1–2 minutes per side. You’re not cooking it through, just giving it a golden crust.
In a bowl, whisk together sugar, vinegar, ketchup, soy sauce, garlic powder, and salt. For a thicker sauce, mix cornstarch and water separately and add it to the sauce.
Transfer browned chicken to the baking dish. Pour the sauce evenly over the chicken and gently toss to coat. Bake uncovered for 40–45 minutes, stirring once or twice to coat the chicken in the sauce as it thickens and caramelizes.
Let rest for 5 minutes. Serve over steamed white rice or fried rice with optional pineapple or bell pepper chunks.