Preheat the oven to 350°F. Line an 8-inch cake pan with parchment paper.
To make the brownies: In a large mixing bowl, add the brown sugar, chocolate, cocoa, and boiling water. Mix on low until combined, and there are no chunks of chocolate, and you have a smooth consistency.
Add in the canola oil, coconut milk, flour, vanilla bean, baking powder, and sea salt in that order. Mix on low until combined, do not over mix. Transfer to the prepared pan and spread evenly.
Bake for 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Allow to cool completely in the pan.
To make the frosting: In the bowl of a stand mixer fitted with the paddle attachment, add the shortening, powdered sugar, and water. Mix on low until combined, and then speed the mixer up to high and mix for 2 to 3 minutes or until light and fluffy.
Divide the frosting into four separate bowls.
To make the pink: Add in ⅛ teaspoon of the pink dye and stir to combine completely. Transfer to a piping bag with Ateco tip #864.
To make the green: Add in a ¼ teaspoon of the green dye and stir to combine completely. Transfer to a piping bag with Ateco tip #846
To make the blue: Add in ⅛ teaspoon of the green dye and ⅛ teaspoon of the blue dye and stir to combine completely. Transfer to a piping bag with Ateco tip #898.
Add the white frosting into a piping bag with Ateco tip #804.
Cut the brownies into 8 triangles.
In a zig zag motion, starting at the top of the brownie triangle, pipe a zigzag with frosting going all the way down. You will use this same motion for the white, green, and blue, they will just look different because of the tips.
For the pink trees, pipe dollops of frosting all the way down the triangle.
On the pink trees, add blue sugar and snowflake sprinkles.
On the white trees, add the rainbow sprinkles.
On the green trees, add the nonpareils.
On the blue trees, add the peppermint crunch.
Store in an airtight container for up to 5 days.