
Preheat oven to 350 degrees and prepare an 11x7 baking dish by greasing with nonstick cooking spray.
In a large bowl, whisk together the gluten free flour, sugar, cocoa powder, baking soda, and salt.
Make a well in the center of the dry ingredients. Pour in the water, oil, vinegar, and vanilla extract. Whisk to combine.
Pour the mixture into the prepared baking dish and bake for 30 to 35 minutes, until a toothpick inserted in the center of the cake comes out clean.
Top with chocolate frosting when the cake has cooled completely.