Cut the chicken into one-inch pieces and salt and pepper. Heat olive oil in a wok or skillet over medium-high heat and add the chicken. Cook until no longer pink and remove and set aside on a plate.
In a small bowl combine the soy sauce, brown sugar, apple cider vinegar, garlic, sesame oil, and ginger. In a separate small bowl whisk the water and cornstarch to make a slurry. Add the cornstarch to the sauce mixture and whisk.
Add the sauce to the skillet and bring to a boil. Reduce heat and whisk until it starts to thicken.
Add the chicken back to the skillet and toss until coated and heated through. Garnish with chopped green onions and sesame seeds. Serve over rice if desired.