Begin by combining 2 tablespoons of cold water with soy sauce, vinegar, Splenda, cornstarch and chili sauce -- stir well until all ingredients have dissolved. Set sauce aside.
Spray a large pan or wok with nonstick spray, and bring to medium-high heat.
Add chicken, mushrooms, bell peppers, celery, onion, garlic and 2 tablespoons of water. Stirring occasionally, cook for about 5 minutes.
Once chicken is almost fully cooked but still tender, add peanuts and water chestnuts to the pan or wok.
Raise heat to high, give sauce a stir, and add it to the pan/wok as well. Mix entire dish until all ingredients are coated in sauce, and the sauce is hot and thick. Season to taste with salt, pepper, and red pepper flakes.