Preheat the oven to 350 degrees Fahrenheit. Spray a 13 X 9 X 2-inch baking dish with non-stick cooking spray.
Cut 2 pounds boneless skinless chicken breasts into bite-sized pieces and place in a large bowl. Crack 1 large egg on top of the chicken and massage it in with your hand to coat the chicken.
Transfer the chicken to a ziplock bag. Add 1 cup cornstarch, seal the bag, and toss to coat the chicken well.
In a large skillet over medium-high heat, add ¼ cup vegetable oil. Working in batches, add the coated chicken and cook until browned. It doesn't have to be fully cooked, just golden on the outside. Place the chicken in the prepared dish.
In a medium bowl, whisk together ¾ cup hoisin sauce, ¼ cup soy sauce, ¾ cup brown sugar, 2 cloves minced garlic, ¼ cup rice wine vinegar, 2 teaspoons sesame oil, ½ teaspoon ground ginger, and 1 teaspoon crushed red pepper.
Pour the sauce over the chicken and bake for 45 minutes. Stir the chicken every 15 minutes so that it is coated in the sauce. Garnish with green onions, serve with rice, and enjoy!
Notes
Leftover Instructions
In the Refrigerator: Store leftovers in an airtight container for up to 4 days. Reheat in a skillet over medium heat or in the microwave until warmed through.
In the Freezer: Transfer cooled chicken to a freezer-safe bag or container and freeze for up to 3 months. Thaw overnight in the refrigerator, then reheat on the stove or in the microwave until hot.