Prepare the Brownies
Prepare the brownie mix according to package directions. Spread the batter evenly in a greased 9x13 inch baking pan. Bake as directed on the package until a toothpick inserted in the center comes out with moist crumbs.
Make the Coconut Layer
While the brownies are baking, combine the shredded coconut, sweetened condensed milk, and powdered sugar in a medium bowl. Mix thoroughly until all ingredients are well incorporated and you have a thick, sticky mixture.
Add Coconut Layer
As soon as you remove the brownies from the oven (while they're still hot), carefully spread the coconut mixture over the top of the brownies. Use a spatula to gently spread it into an even layer, covering the entire surface.
Prepare the Chocolate Topping
Place the container of chocolate frosting in a microwave-safe bowl. Heat in the microwave for 20-30 seconds, or just until the frosting becomes pourable but not too hot. Stir until smooth.
Finish the Brownies
Pour the warm chocolate frosting over the coconut layer. Quickly spread it to cover the entire surface, making sure to seal the edges. This will help keep the coconut layer moist and prevent it from drying out.
Cool and Set
Allow the brownies to cool completely at room temperature, then refrigerate for at least 1 hour before cutting to allow all layers to set properly.