Preheat oven to 350° F and grease a 18x13'' pan, or line with parchment paper.
In a medium size sauce pan add margarine, water and cocoa powder and mix well using a wire whisk.
Add in flour, and sugar and mix until blended.
Finally add in baking soda, salt, buttermilk, cinnamon, vanilla, eggs and mix well.
Pour mixture into prepared pan and smooth with a spatula to make sure it is dispersed in an even layer.
Bake for 30-35 min.