For the Marinade & Sauce:
½ cup hoisin sauce
¼ cup white vinegar
3 tablespoons soy sauce
3 tablespoons sugar
2 tablespoons cornstarch
1½ cups water
4 boneless, skinless chicken breasts (about 1½ pounds), cut into 1-inch pieces
1 tablespoon vegetable oil
4 garlic cloves, minced
2 tablespoons grated fresh ginger
½ teaspoon crushed red pepper flakes

For Coating & Frying:
3 egg whites
1½ cups cornstarch
½ cup all-purpose flour
½ teaspoon baking soda
4 cups vegetable oil
1-2 green onions, thinly sliced (optional, garnish)