Trim any fat off of the chicken and cut the chicken breasts into 1-inch pieces. In a medium bowl, mix together 4 tablespoons of the corn starch with the salt and pepper; add the chicken and toss well to completely coat.
In a large skillet or pot, heat half of the oil over medium-high heat. Once the oil is hot, add half of the chicken pieces and cook on one side without stirring for 3 minutes. Turn each piece of chicken and cook for an additional 3 minutes.
Remove the cooked chicken from the skillet and set aside. Add the remaining half of the oil to the skillet, then add the remaining pieces of uncooked chicken. Cook the chicken on one side without stirring for 3 minutes, then flip and cook for an additional 3 minutes. Remove the chicken from the skillet and set aside.
Add the minced garlic to the skillet and sauté for 20-30 seconds until fragrant. To the skillet at the water, soy sauce, apple juice, chicken broth, ketchup, bourbon, vinegar, brown sugar, ground ginger, onion powder, and red pepper flakes. Stir well and bring the mixture to a boil over medium-high heat.
Reduce the heat to low and add the chicken to the sauce. Simmer for 10-15 minutes until the sauce is reduced by half.
Mix the remaining 1 tablespoon of corn starch with 1-2 tablespoons of water, then stir into the sauce to thicken (optional).
Serve the bourbon chicken hot over steamed rice.