Preheat the oven to 350°F. Grease a 9x13-inch baking dish and set aside.
In a bowl, toss the 1 pound chicken pieces with 1/2 teaspoon salt and 1/2 teaspoon ground pepper until evenly seasoned.
Place the 1 cup cornstarch in a shallow dish and the 2 beaten eggs in another shallow dish. Working in batches, dredge each seasoned chicken piece in the cornstarch, shake off excess, then dip into the beaten eggs. Place coated pieces on a plate.
Heat the 3 tablespoons oil in a large skillet over medium-high heat. Add the coated chicken in a single layer (work in batches if needed) and cook 4–5 minutes, turning so pieces brown on all sides. Transfer browned chicken to the prepared baking dish.
In a medium bowl, combine 1/2 cup orange juice and the 1 teaspoon cornstarch; whisk until the cornstarch is dissolved. Add 1/2 cup brown sugar, 2 tablespoons rice vinegar, 1 tablespoon soy sauce, 1 teaspoon finely chopped garlic, 1 teaspoon red chili flakes, 1 teaspoon orange zest, and 1 teaspoon salt. Whisk until smooth and evenly combined.
Pour the orange sauce over the chicken in the baking dish, spreading so the chicken is coated.
Bake uncovered for 40–50 minutes, stirring gently every 15 minutes, until the sauce is thickened and the chicken is well coated.
Remove from the oven, sprinkle the 2 tablespoons green onion over the chicken, and serve warm.