First off, get your quinoa cooking. Once you have that started, heat up the sauté pan on high (8/10) with the olive oil, until smoking. Add your chicken and brown on all sides, 4-5 minutes. Meanwhile, in a 2 cup measuring glass, mix soy sauce, sherry, brown sugar, vinegar, sesame oil, and cornstarch. Fill to the 1cup mark with water. Stir and set aside.
Once the chicken has browned, add in garlic, ginger and bell pepper. Stir around for 2-3 minutes, until bell pepper has started to soften.
Turn down the heat to medium-high (6/10) and add sauce mixture. Stir around really well, don't let it sit for too long or you'll have burned soy and sugar, not so tasty.
Add cashews and water chestnuts and heat through, and the sauce has thickened, about 2 minutes.
Serve over quinoa, top with sesame seeds and green onion.