Melt coconut oil over a very low heat. Remove from heat. Stir in carob, sweetener, and peppermint extract. (If you heat over too high of a heat or don't remove from the heat, the coconut oil will separate from the carob when cooling. You can still eat it, but it won't be as smooth and the chips will be kind of mottled, depending on how bad they separated.)
Spread mixture into a pan (8x8 works well).
Place in refrigerator or freezer until solid. Remove from pan, and cut into chunks of desired size with a good, solid knife.