In a small bowl, combine the chicken, egg whites, 2 tablespoons of cornstarch and 2 tablespoons of soy sauce. Mix well and set aside.
In another small bowl, combine the chicken stock, chilies, dry sherry, vinegar, remaining soy sauce and 2 teaspoons of the cornstarch. Mix well to dissolve the cornstarch and set aside.
In a flat-bottom wok, heat the vegetable oil to about 330°F. (If you do not have an oil thermometer, test oil temperature by frying a small cube of bread. If the bread turns golden brown in about 60 seconds, the oil is hot enough). In small batches, fry the marinated chicken pieces until brown, crispy and cooked through. Remove and drain on a paper towel.
Pour off all but 2 tablespoons of the oil from the wok. Stir-fry the red or green peppers, green onions, garlic and nuts for 30 seconds. Add the crispy chicken.
Using a spatula or spoon, push the stir-fried vegetables up along the sides of the wok, creating an empty well in the bottom. Turn heat to high then pour the reserved stock mixture into the well. Bring to a boil and cook until sauce begins to thicken. Toss all ingredients together in the pan.
Serve immediately with sticky or plain rice.