For Brownies: Preheat oven to 350 degrees F (325 F for glass or dark pan).
Liberally spray a 9-inch square pan with non-stick spray.
In a large bowl, whisk mashed avocado and melted chocolate.
Whisk in sugar until combined, then add eggs and vanilla extract, mixing well.
Add in flour, cocoa, baking powder, and salt, mixing with a large spoon or rubber spatula until JUST combined - do not over mix.
Stir in oil until its well distributed and batter is somewhat smooth. Fold in chopped chocolate, then spread batter in pan.
Bake for 28-32 minutes (35-40 minutes if baking at the lower temperature) or until middle is set.
Remove and let cool completely, then frost and top with grated chocolate if desired.
For Frosting: Add avocado to the bowl of an electric stand mixer (or a hand held electric mixer) and beat until creamy. With the mixer on low speed, add in vanilla and then slowly add in powdered sugar and cocoa powder, scraping down the sides if needed, until a smooth frosting forms.