Place the cashews on a baking sheet in one layer. Toast for around 5 minutes, or until fragrant.
In a medium bowl, toss the chicken in the cornstarch, salt and pepper until coated.
Heat 1 tablespoon of avocado oil in a skillet over medium high heat. Cook ½ of the chicken for around 3 minutes, or until lightly browned. Transfer to a plate.
Heat the remaining oil and chicken, and cook for around 3 minutes until lightly brownied. Return the first batch of chicken to the pan. Reduce heat to medium and add in the rice vinegar.
Add in the hoisin sauce, soy sauce, water and red pepper flakes. Cook until chicken is cooked through. Remove from heat and mix in the cashews and sesame oil.