Beat egg in a bowl. Mix flour, cornstarch, and salt in a bowl.
Dunk chicken in egg mixture, then flour mixture, then add to hot oil and fry until golden brown and chicken cooked through. Set aside on a paper towel. --FOR THE GENERAL TSO SAUCE--
Whisk together chicken stock, sugar, rice wine vinegar, hoisin, sesame oil, Sriracha, dark soy sauce and cornstarch in a medium sized bowl. Set aside.
Add oil to a pan and add scallion, ginger, and garlic and cook for 1-2 minutes or until fragrant. Add mixture from step one and bring to a boil.
Let the sauce cook for a few minutes until thickened. Add fried chicken and toss to coat. Sprinkle with toasted sesame seeds and set aside. --FOR THE ASIAN SLAW--
Mix all ingredients in a large bowl and set aside. --FOR THE SANDWICH--
Toast buns and place the General Tso fried chicken on top of the bottom bun. Next, add Asian slaw, a drizzle of mayo and the top bun. Serve immediately.