Heat vegetable oil in a deep fryer or large pan until it reaches 375°F (190°C), ensuring the oil is hot enough for frying.
In a large bowl, whisk the egg and then add the chicken, salt, sugar, and pepper, mixing thoroughly. Gradually stir in the cornstarch, ensuring each piece of chicken is evenly coated.
In batches, gently add each piece of chicken to the hot oil. Fry for about 3 minutes, or until golden brown and floating. Transfer the cooked chicken to a plate to cool while frying the next batch.
After frying all the chicken, refry each batch, beginning with the first one. Fry for an additional 2 minutes, or until the chicken reaches a deep golden brown. Let the chicken drain on a paper towel-lined plate.
For the sauce, heat vegetable oil in a wok or large skillet over high heat. Add the green onion, garlic, whole chiles, and orange zest, stirring constantly. Cook for 1 to 2 minutes until the garlic becomes golden and the chiles intensify in color.
Stir in the sugar, soy sauce, chicken broth, peanut oil, rice vinegar, sesame oil, and ginger, then bring the mixture to a boil. Let it simmer for 3 minutes. Meanwhile, dissolve 2 teaspoons of cornstarch in water, then whisk it into the boiling sauce. Allow the sauce to return to a boil and cook for about 1 minute, until it thickens and becomes clear.
Add the chicken to the boiling sauce and lower the heat to a simmer. Cook for about 3 minutes, allowing the chicken to heat through and soak up some of the sauce.