Begin by combining the chicken marinade ingredients that will be used for velveting the chicken. Stir together vegetable oil, cornstarch, egg, salt, sesame oil, rice wine vinegar in a medium sized bowl and add diced raw chicken. Allow chicken to marinate in the fridge for 30-60 minutes.
While chicken is marinating, cut up your zucchini, bell pepper, onions, and green onions into small bite-sized pieces. I like to use both the whites and the green parts of the green onions.
Prepare your kung pao sauce by whisking together minced garlic, water, soy sauce, rice wine vinegar, brown sugar, oyster sauce, grated ginger, and cornstarch. Set to the side.
Heat wok or large stir fry pan on medium-high heat and add additional 1 tbsp. of oil. Add coated chicken pieces and stir fry until they start to brown on the outside and are almost cooked through, 8-10 minutes.
Remove chicken to a side plate and add final tablespoon of oil. Turn heat to high and add in zucchini, bell pepper, onion, and green onion. Stir fry quickly on high heat for 4-5 minutes and then remove to the side next to the chicken.
To the empty wok, add dried chilis and peanuts and cook until peppers are fragrant (1-2 minutes). The peanuts will get a little color to them as well.
Stir in kung pao sauce and allow to thicken and deepen in color for 1-2 minutes.
Add back in vegetables and chicken pieces and stir to coat. Cook until sauce is thickened and the chicken is cooked through.