In a medium bowl, combine sesame oil, soy sauce, oyster sauce, 1 tbsp corn starch, water vinegar, granulated sugar, 3 cloves minced garlic, ginger, Five Spice, and red pepper flakes. Whisk well to combine and set aside.
Slice the chicken breast into thin strips and season with the remaining cornstarch, salt and black pepper.
To a hot dry pan add the cashews and toast, stir and move until brown and toasted, then remove and set aside
Add 2 tbsp vegetable oil to a heated pan, Add the chicken to an oiled pan and cook until the chicken is about 90% done, remove from the pan (it will finish cooking in the sauce).
Add the remaining vegetable oil to the pan, add the broccoli and remaining 3 cloves minced garlic to the pan and cook just for a few minutes.
To the saute broccoli, add the sauce, chicken and roasted cashews to the skillet. Simmer for a minute or two, just to give the sauce time to heat up and thicken slightly. Then serve