In a medium bowl, whisk together the eggs.
In a separate bowl, combine the cornstarch, salt, and black pepper.
Dip the chicken pieces into the egg, then coat evenly with the cornstarch mixture. Set aside on a plate.
Heat the vegetable oil in a large skillet over medium-high heat.
Add the coated chicken pieces in a single layer and cook for 3-4 minutes per side until golden brown and cooked through. Work in batches if necessary to avoid overcrowding.
Remove the cooked chicken from the skillet and place on a paper towel-lined plate to drain excess oil.
In the same skillet, combine the orange juice, granulated sugar, soy sauce, rice vinegar, grated ginger, minced garlic, orange zest, and crushed red pepper flakes.
Bring the sauce to a simmer over medium heat, stirring occasionally.
Once simmering, stir in the cornstarch slurry and cook for 1-2 minutes until the sauce thickens.
Return the cooked chicken to the skillet and toss to coat evenly with the orange sauce.
Remove from heat and let cool completely before transferring to an airtight container for storage.
To serve, reheat the orange chicken in a skillet over medium heat until warmed through.
Garnish with sliced green onions and toasted sesame seeds before serving.