In a small saucepan heat the sweetener over medium heat, stir frequently, until it is melted. Turn the heat off and whisk in the cocoa powder.
Drizzle the syrup over the cereal in a large bowl. Toss, scraping the bottom and sides of the bowl with a rubber spatula, until all the cereal has chocolate on it.
Spread on a baking sheet lined with wax paper to dry.