Cut 4 boneless skinless chicken breast into bite-sized pieces. In a medium-sized mixing bowl, whisk together 4 large egg whites, 2 tablespoons cornstarch, 1 teaspoon salt and 1/2 teaspoon white pepper. Submerge chicken breast pieces in mixture and set aside.
Meanwhile, pour enough vegetable oil into a large pot or saucepan to cover the bottom with 2 inches of vegetable oil Heat to 350 degrees F. Working in small batches, fry chicken pieces until cooked through and golden brown, about 3 to 4 minutes. Remove from oil and drain on a paper towel-lined plate.
In a large skillet, whisk together 1/4 cup of the water with the 2 tablespoons cornstarch until dissolved. Whisk in the remaining 1/2 cup of water along with 1/4 cup rice vinegar, 3 tablespoons brown sugar, 2 tablespoons soy sauce, 2 tablespoons hoisin sauce, 1 tablespoon minced garlic, 1 teaspoon ground ginger, and ½ teaspoon crushed red pepper flakes. Place the skillet over high heat and bring to a simmer. The sauce will thicken upon simmering. Let simmer up to 2 minutes, then turn off the heat. Add in chicken and toss to coat.
Serve immediately. Garnish with 1/4 cup sliced green onion (if using).
Notes
Serving Suggestion: General Tso's chicken is great served over rice with steamed veggies like broccoli.