Preheat the oven to 325°F (165°C).
In a small bowl or saucepan, combine sugar, apple cider vinegar, ketchup, and soy sauce. Set aside.
In one bowl, mix cornstarch, salt, pepper, and garlic powder.
In a separate bowl, beat the eggs.
Heat oil in a skillet over medium heat.
Coat chicken pieces first in the cornstarch mixture, then in the eggs.
Add to the skillet and cook 1–2 minutes per side, until golden brown.
Use a 9x13-inch dish (or similar). Arrange chicken in a single layer and pour the sauce over the top.
Place in the oven and bake until the sauce thickens and the chicken is cooked through, turning the chicken every 25 minutes. Sauce thickening time may vary depending on your oven, usually 15–45 minutes. Remove as soon as the sauce is glossy and thickened.
This recipe is perfect with steamed broccoli and rice for a complete meal.