Place a large non-stick skillet over medium-high heat, add 1 tbsp. oil. When the oil is hot, add the chicken (you may need to do two batches depending on the size of your skillet) and season with salt and pepper. Cook until lightly browned but not cooked throughout, about 3-4 minutes. Transfer to a plate and repeat if needed.
Add the remaining vegetable oil to the skillet, when the oil is hot add the garlic and the white parts of the green onion, cook for a few minutes or until the onion is translucent (taking care not to burn the garlic), then add in the chicken. Turn the heat down to medium and add in the rice vinegar, hoisin sauce, soy sauce, water and sesame oil (add a few drops of Sriracha if desired). Cook for about 2 minutes, stirring continuously, then add in the green parts of the onion and the cashews. Serve immediately.
Notes
-This recipe is best the day of, the cashews tend to get soggy if left overnight.