Preheat oven to 350 degrees F. Liberally grease a 9x13 rectangular baking pan with cooking spray and set aside.
In a large bowl, whisk together the flour, cocoa powder, baking soda, salt, and granulated sugar until combined. Add in the oil, vanilla, vinegar and room temperature coffee OR water and whisk together until a soft, smooth batter comes together. Pour into the prepared pan.
Bake for 30-40 minutes or until a toothpick inserted near the center comes out clean or with moist but not wet crumbs. Cool completely.
For the glaze: In a medium bowl, whisk together the confectioners' sugar, cocoa powder, vanilla and 2 Tablespoons of coffee OR water until a soft, pourable glaze comes together. If glaze is too thick, add more water, one Tablespoon at a time. Pour the glaze over the cooled cake and spread it into an even layer. Allow the glaze to set, about 20 minutes, before cutting into squares.