Chop the chicken into bite-sized pieces and pat dry. Toss with 1 tbsp cornstarch until lightly coated, shaking off any excess.
Heat 2 tbsp sesame oil in a skillet over medium heat. Add the chicken in a single layer and cook for 6–8 minutes until no longer pink. Drain excess liquid, then cook another 3–4 minutes until lightly golden.
In a bowl, whisk together pepper, onion powder, apple juice (or bourbon), ketchup, soy sauce, water, brown sugar, ground ginger, minced garlic, and 1 tsp cornstarch until smooth.
Pour the sauce into the skillet with the chicken. Scrape up any browned bits from the pan and bring to a gentle boil over medium heat.
Reduce heat to low and simmer for 5–7 minutes, stirring occasionally, until the sauce thickens and coats the chicken. Add a splash of water if it becomes too thick.
Turn off the heat and let sit for 5 minutes. Garnish with sliced green onions before serving.