In a small bowl, combine bite sized chicken pieces, cornstarch, 1 tablespoon of soy sauce, and black pepper. Stir to combine and set to the side.
In a large skillet with a lid, add a drizzle of sesame oil. Add in green bean pieces, sliced mushrooms, and diced onion. Allow to cook over medium-high heat for about 3-4 minutes. Stir occasionally.
In another small bowl, whisk together remaining soy sauce, honey/brown sugar, ginger, minced garlic, and rice vinegar.
Remove vegetables from skillet. Add another drizzle of oil and add in prepared chicken. Cook for 4 minutes, until outside is browned (will continue cooking in later steps).
Return green bean mixture to the skillet. Pour in soy sauce mixture and cashew pieces and stir.
Cover the skillet and allow to cook for another 10 minutes, or until the chicken is no longer pink in the center.
