Preheat the oven to 350 F. In a medium bowl, whisk together flour, cocoa powder, salt, and baking soda. In a large bowl, combine butter with sugar until fluffy.
Add in the egg and vanilla extract and mix until smooth. Add in the flour mixture, mix until it is fully combined. Add in the green food coloring, and mix until it is fully green.
In a shallow dish, combine granulated sugar and ground cinnamon. Roll the cookie dough into balls, then roll each one into the cinnamon sugar mixture.
Place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes.
