Dice zucchini, bell peppers, garlic, and green onions. Place in a bowl. Drain tomatoes from can then place in vegetable bowl; set aside.
Cut chicken breasts into strips then cut into cubes. Place in large plastic bag or bowl. Add in wet marinade ingredients then toss together. Add cornstarch and shake to coat well.
Using 2 medium skillets, pour 1.5 tablespoons oil into each. Heat over medium heat. Add chicken to skillets. Be sure to not crowd skillets. It works best to use 2 skillets for this step as you don’t want the chicken to steam and become soft.
Cook chicken until golden brown then flip chicken and repeat. This should take about 10-15 minutes, total.
Meanwhile, make the Kung Pao Sauce. In a small bowl, combine sauce ingredients and whisk well to combine.
Remove chicken to small bowl.