In a bowl, combine egg and cornstarch and season with a little salt and pepper. Add chicken pieces and marinade for 5 minutes.
Add all the ingredients for the sauce into a bowl and whisk until well blended.
In a large pan over medium high heat, add 1 tbsp vegetable oil. Drop chicken pieces and cook until both sides are golden brown. Remove chicken from the pan and set aside.
Add remaining 1 tbsp vegetable oil to the pan (still over medium high heat) and add garlic and ginger. Cook for 1 minute and add onions, green and red bell pepper and shiitake mushrooms. Cook for 5 minutes.
Return chicken to the pan and add sauce. Stir and coat vegetables and chicken for 1 minute and turn the heat off.
Transfer to a plate or bowl and serve Szechuan chicken with a side of white rice.
This Szechuan Chicken Recipe will keep refrigerated for up to 3 days.