Toss the chicken pieces in a bowl with the soy sauce. In a separate bowl, whisk the cornstarch and egg together to form a batter.
Heat the oil in a wok. Dip the chicken into the batter and fry over a high heat for 4 to 5 minutes until golden and crisp and just cooked. Scoop out with a slotted spoon and set aside on a plate lined with paper towels.
Add the chiles and peppers to the pan and fry for 3 to 4 minutes before adding all the sauce ingredients except, for the cornstarch. Simmer over a high heat for 5 minutes, then blend 2 to 3 tablespoons of the sauce with the remaining cornstarch in a cup until smooth. Return to the pan and bubble until the sauce thickens.
Return the chicken to the pan and simmer for 2 to 3 minutes until the chicken is sticky and coated. Serve in deep bowls.
Meanwhile steam the zucchini batons for 2 to 3 minutes, then divide between four bowls. Serve with the hot and sour chicken.