In a bowl, mix together the soy sauce, vinegar, brown sugar, oyster sauce and sesame oil. Set aside.
Heat the vegetable oil in a large skillet over high heat and add the chicken in a single layer. Sprinkle with a SMALL amount of salt, then leave it alone for a few minutes to give the chicken a chance to brown. When the chicken is golden on one side, flip it to brown the other side.
Lower the heat to med-low, then add garlic and ginger, stir to combine. Stir in bell pepper, cook 2-3 minutes.
Pour in sherry and scrape the bottom of the pan to release all the flavorful bits. Pour in the sauce mixture, then mix the cornstarch with 1/4 cup of cold water to make a slurry, then mix that in. Stir sauce 1-2 minutes to thicken.
Add water chestnuts and cashews, stir to coat everything with the sauce. Add a splash of chicken broth if your sauce is too thick.
Serve with white rice, garnish with sliced green onions and toasted sesame seeds.