Preheat oven to 350°F. Butter and flour a Bundt pan.
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda and salt. Set aside.
In a separate large bowl, whisk together vegetable oil, avocado, water, vanilla and mint extract. Whisk in granulated sugar until combined.
Add wet mixture to dry mixture. Stir in until combined and smooth.
Pour batter into greased Bundt pan. Sprinkle with dark chocolate chips. Bake for 45 to 55 minutes, or until set in the center.
Let cake cool for 15 minutes and turn out onto a cooling rack until completely cooled.
In a medium saucepan, melt chocolate and butter together over low heat. Whisk in sugar.
Stir in water 1 tablespoon at a time, until combined. Then stir in vanilla.
Drizzle chocolate frosting over cake and allow to set for at least 20 minutes.
Slice and serve!