Preheat your oven to 350°F (175°C). Grease an 8-inch round baking pan and line the bottom with parchment paper.
In a food processor, combine the drained black beans, oat flour, cocoa powder, maple syrup, melted coconut oil, vanilla extract, baking powder, and salt. Blend until the mixture is smooth and well combined
Pour the brownie batter into the prepared pan. Smooth the top with a spatula. Bake in the preheated oven for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Allow the brownie to cool completely in the pan. Once cooled, remove it from the pan and place it on a cutting board. Cut the brownie into 8 equal quarters, forming triangular Christmas tree shapes.
In a heatproof bowl, melt the dairy-free dark chocolate chips using a double boiler or in the microwave in 30-second intervals, stirring between each interval until smooth.
Place a sheet of parchment paper under the brownie trees. Using a spoon or a piping bag, drizzle the melted dark chocolate over the Christmas tree brownies to create the appearance of tree branches. Add a little "stick " of candy cane to use for the "trunk" of the tree.
While the chocolate is still melted, decorate the trees with gluten-free and dairy-free Smarties or other candy of your choice. Allow the chocolate to set.