Make the cake: Preheat oven to 350F (180C). Grease a 8-inch (20cm) round cake pan and set aside.
In a large bowl, stir flour, cocoa powder, baking soda, salt and sugar.
Add water, oil, vinegar and vanilla extract. Stir until combined.
Pour the batter into prepared pan and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Allow to cool for 10 minutes, release from the pan, then let to cool to room temperature.
Make the frosting: chop the chocolate into small pieces and place in a heatproof bowl. Set aside. In a small saucepan heat the coconut milk, pour hot coconut milk over the chocolate and let sit for 2 minutes, then mix until melted and smooth.
Chill in the fridge for about 30-60 minutes or until set, beat the frosting until fluffy and frost the cake as desired.