Whisk the sauce ingredients. In a small bowl, whisk together the sauce ingredients until the corn starch is dissolved and no clumps remain. Set aside.
Season the chicken. In a mixing bowl, toss the chicken pieces with cornstarch, salt, and pepper until well-coated. Set aside while the oil heats.
Fry the cashews. Heat the oil and sesame oil in a wok over medium heat and once the oil is hot and shimmering, add the cashews. Cook, stirring constantly, until the cashews are golden brown. Use a slotted spoon to remove them from the oil to a paper towel lined plate and season with salt.
Fry the chicken. Increase the heat to medium-high. Add the chicken to the wok and spread it out in a single layer in the wok. Cook, without moving the chicken, until golden brown on one side, and then flip and cook on the other side. Use a slotted spoon to remove the chicken from the pan and transfer to a plate.
Saute the veggies and aromatics. Add the garlic and serrano to the remaining oil in the wok. Cook for about 1 minute, until fragrant. Add the chopped onion, bell pepper, zucchini and chopped green onions to the wok. Cook, stirring occasionally, until the veggies are soft.
Add the chicken and cashews. Add the chicken and cashews back to the pan and add the sauce. Bring to a simmer until the sauce is thick and toss to coat well. Season to taste with any salt and pepper and serve hot with steamed rice.