Spray slow cooker with non-stick cooking spray. Place chicken (frozen, thawed or fresh) inside slow cooker. Mix together brown sugar, vinegar, soft drink, garlic, soy sauce and pepper together. Pour over chicken. Cook on low for 6-8 hours or high for 4 hours.
Take chicken pieces out of slow cooker (mine basically fell apart) and pour remaining sauce into saucepan. Place saucepan over high heat. Mix together corn starch and water, pour into saucepan and mix well. Let sauce come to a boil and boil for 2-3 minutes, or until it starts to thicken and turns into a glaze. Remove from heat and let sit for a minute or two (it will continue to thicken as it cools down).
Sprinkle red pepper flakes on top if desired. This can be served over rice or pasta, I also like it with a baked potato on the side. (It's good on top of the potato too!)