Heat a large skillet over medium high heat. Add vegetable oil. Place chicken pieces to skillet and cook and stir for about 10 minutes, or until no longer pink.
Drain any juices. Return skillet to stove top and continue cooking over medium high heat.
In a medium mixing bowl combine garlic, apple or pineapple juice, brown sugar, ketchup, apple cider vinegar, water, soy sauce, a pinch of red pepper flakes and cornstarch. Whisk it all together until the cornstarch is dissolved and all ingredients are well combined.
When chicken is golden brown pour sauce into the pan. Stir it around to cover all the chicken. Reduce heat to a low and cover pan with the lid at an angle to allow some of the steam to escape. Simmer 20 minutes, stirring a couple of times during the cooking period.
Serve over white or brown rice. Enjoy!