To make this Kung Pao Chicken, start by preparing the sauce. Add all of the sauce ingredients to a medium-sized bowl or large measuring cup and whisk until they're fully combined. Then, set it aside.
Prepare the chicken by patting it dry with a paper towel and slicing it into bite-sized cubes.
Then, wash and chop the bell peppers and and zucchini and chop them into small pieces. Be sure to remove the seeds from the bell peppers.
Next, heat a large skillet, on the stove, over medium-high heat, and add in two tablespoons of the oil.
Once the oil is hot, add in the chicken and sauté it for about 4 minutes, until it is just cooked on the outside. It might still be pink on the inside, but that is okay - it will continue to cook later on.
Remove the chicken from the pan and set it aside to rest. Then, add the remaining two tablespoons of oil to the same pan.
Add the chopped bell peppers and zucchini to the pan, alongside the garlic, peanuts, and chili peppers, if using. Sauté them for about 3 minutes.
Then, pour in the sauce, and stir to coat well.
Add the chicken back into the pan and stir to coat it in the sauce.
Then, reduce the heat to low, place the cover on the pan, and allow it to cook for 5-6 minutes, until the chicken is fully cooked through.
Once it's done, remove it from the heat, serve over rice, and enjoy!