Season the chicken pieces with salt and pepper. Set up a breading station by placing flour in one bowl, beaten eggs in another, and breadcrumbs in a third bowl.
Dredge each piece of chicken in flour, dip in the beaten eggs, and then coat with breadcrumbs. Set aside on a plate.
In a large skillet or wok, heat vegetable oil over medium-high heat. Once hot, add the breaded chicken pieces in batches to prevent overcrowding.
Fry the chicken pieces for about 4-5 minutes on each side, or until golden brown and cooked through. Remove them from the skillet and place them on a baking sheet lined with foil to keep warm.
In the same skillet, reduce the heat to medium and add the fresh orange juice, orange zest, sugar, soy sauce, and rice vinegar. Stir well and bring to a simmer.
Add the cornstarch mixture to the sauce and stir continuously until the sauce thickens, about 1-2 minutes.
Add the fried chicken back into the skillet and toss to coat it evenly with the orange sauce. Cook for another 2-3 minutes until well combined.
Transfer the orange chicken to a serving dish. Garnish with chopped green onions and sesame seeds if desired. Serve hot with steamed rice or noodles.