If you prefer roasted cashews, fry them in an unoiled skillet over medium-high heat, stirring often until roasted, about 5 minutes. Remove from the skillet; set aside.
Add the vegetables and fry, stirring often, until vegetables are a little crisp but slightly tender.
For a thick sauce, bring back to a boil while combining 1 tablespoon cornstarch with 1 tablespoon water. Once the sauce boils again, stir in the cornstarch mixture/slurry. If desired to coat cashews in sauce, stir them in now. If not hold them for garnish.
*This dish is traditionally made with oyster sauce, but since I didn't have any on hand I used fish sauce since it is also salty. Fish sauce did not impart a fish flavor in this dish.
For a lower-calorie version, do not coat chicken in cornstarch.