Preheat oven to 350F. Grease and flour a 9-inch round cake pan or an 8-inch square pan.
In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt. Add oil, vanilla, and water. Mix until ingredients are just combined.
Pour batter in pan.
Bake for 30 to 35 minutes or until a toothpick inserted near the center comes out clean. Let cake cool completely on a rack. Cut cake into 1-inch cubes.
Meanwhile, combine Cocowhip™ in a bowl with peppermint extract.
To assemble the trifle, arrange half of the cake cubes in a single layer in a large trifle bowl or individual cups. Drizzle half of the chocolate syrup over the cake layer and cover with a layer of peppermint whipped cream. Sprinkle with some crushed peppermint candy over the whipped cream. Repeat with another layer of cake, then chocolate syrup, and end with a final layer of peppermint whipped cream and more crushed peppermint candy on top.
Refrigerate, covered, until ready to serve.