Start by mixing the sauce. Combine soy sauce, oyster sauce, sugar, and dissolved cornstarch in a small bowl. Stir well until the sugar is dissolved and the mixture is smooth. Set it aside so the flavors can meld while you prep the rest.
Next, cut the chicken into bite-sized cubes. Season with salt and pepper, then toss with flour in a mixing bowl. The flour helps the chicken get a nice golden coating when fried. Set the coated chicken aside while you prep the veggies and cashews.
Toast the cashews in a skillet with 1 tablespoon of vegetable oil over medium heat. Stir frequently until they’re golden and fragrant. This step brings out their rich flavor. Remove the cashews and set them aside for later.
In the same skillet, add the sesame oil and the remaining tablespoon of vegetable oil. Increase the heat to medium-high and add the floured chicken. Cook the chicken for about 5 to 7 minutes or until golden brown on all sides and fully cooked through. Once done, transfer the chicken to a clean plate.
Now add the bell peppers and quartered onion to the skillet. Stir-fry them for 2 to 3 minutes. The goal is to keep them slightly crisp while softening the edges. Then toss in the white parts of the green onions and minced garlic. Cook for another minute to build more flavor into the base.
Give the prepared sauce a quick stir and pour it into the skillet with the veggies. Stir constantly as the sauce begins to thicken. This should take about 2 to 3 minutes. You’ll know it’s ready when the sauce becomes glossy and coats the back of a spoon.
Return the cooked chicken to the pan and stir everything together. Make sure all the chicken pieces and veggies are well-coated in the thickened sauce. Finally, toss in the green parts of the green onions and the toasted cashew nuts. Stir just until everything is combined and heated through.
Serve hot with a side of steamed rice or noodles. Enjoy!