In A Skillet, Saute Onion In Oil Until Tender. Add Chicken; Brown On All Sides. Carefully Add Cola, Ketchup, Garlic Powder, Salt And Pepper. Cover And Simmer For 25-30 Minutes Or Until Chicken Juices Run Clear. Remove The Chicken And Keep Warm. Combine The Cornstarch And Cold Water Until Smooth; Add To The Skillet. Bring To A Boil; Cook And Stir For 2 Minutes Or Until Thickened. Return Chicken To Pan; Heat Through.