In a large bow, whisk together 2 cups graham flour, 1 1/4 cups granulated sugar, 1/2 cup oat flour, 1 cup natural unsweetened cocoa powder, 2 teaspoons baking powder, 2 teaspoons baking soda, and 1/2 teaspoon kosher salt until well combined. Add 1/2 cup coconut oil and use your hands to rub it into the dry ingredients until fully incorporated. At this point, you can store the mixture at an airtight container or jar. It will last for a month at room temperature or 3 months in the freezer.