It appears that "Chinese" cashew chicken is really a dish created by an American-Chinese in the early 1960s for American palates.
The original recipe I started with was pretty close to perfect. Up front, I added some more vegetables for color and flavor (and because I see them in restaurant cashew chicken). Afterward, I added the celery and water chestnuts too.
The important practice to embrace is not over-cooking chicken, onion, garlic, bell peppers, celery or water chestnuts. Add no salt whatsoever because there's already so much in the cooking wine, oyster and soy sauces and cashews. If you decide you want to lighten the sauce, hold back a little on the oyster sauce.
Like most Chinese fare, if you prepare everything ahead of time and do a proper mise en place, this goes so fast you can execute it with your guests already at the table and serve it host and fresh. Don't forget the rice.
Seriously, this is one of my best dishes (if not the best). Of course, you have to like what's in it. I have also reheated this dish (rice separately) with care in the microwave and it's really good the next day too.
I multiplied this recipe by 3 (because 3 pounds of chicken and 7 people to feed) and used one whole green and one whole red bell pepper—just under ½ pound of meat per person, which would be a bit excessive if there are other courses to your dinner. Another time, I multiplied by 4; it still worked perfectly.
This went well, except that it was necessary to cook the chicken just a bit longer because of congestion (too much at once) in my wok. Because of that, I also cooked my onion and garlic to a separate large pot from the chicken in order to avoid burning them. I added them back in once all the chicken was ready. This goes pretty fast even if you're cautiously batching the chicken.
1. Mix cornstarch and soy sauce until no lumps. Then add remaining ingredients and mix.
2. Put chicken into large zip-lock bag with baking soda and toss well. Add in 2 tbsp sauce, mix to coat. Set aside for 10-20 minutes.
3. Heat oil over high heat in a wok or skillet. Add the onion, cook for 1 minute, then add garlic and cook for 30 seconds more.
4. Add chicken and cook for 2 minutes.
5. Add bell peppers and other vegetables, cook only for 1 minute.
6. Add remaining sauce/marinade and water. Bring to simmer and cook, stirring, for 1 more minute; sauce will thicken.
7. Stir in cashews, remove from stove and serve immediately with steamed rice.