Preheat oven to 350°F (175°C).

Sift flour and sugar together in a large bowl and set aside.

In a saucepan, combine oleo, cocoa, and water.

Bring the mixture to a boil, stirring constantly.

Pour the boiling mixture over the flour and sugar mixture.

Add eggs, buttermilk, soda, cinnamon, and vanilla to the bowl.

Mix all ingredients well until a smooth batter forms.

Grease and flour a 13 x 9-inch baking pan.

Pour the batter into the prepared pan.

Bake in the preheated oven for 30 to 35 minutes.

Check for doneness by inserting a toothpick into the center; it should come out clean.

Let the cake cool in the pan for a few minutes before slicing and serving.