Preheat the oven to 350°F (175°C). Spray a 10-cup (2.4 l) Bundt pan with cooking spray.
Sift the flour, baking powder, cinnamon, sugars and salt into the bowl of a stand mixer, or a medium-sized bowl if you’re using an electric hand mixer. Add the desiccated coconut and whisk together.
In a liquid measuring cup, lightly whisk together the coconut milk, rum, eggs, and vanilla. Add the butter and coconut oil to the flour mixture, fit the stand mixer with the paddle attachment and mix on low speed until you get a sand like texture and there are no traces of flour, 2 to 3 minutes.
Add the mashed banana and the coconut milk mixture to the flour mixture in 3 equal batches to avoid splashing and overmixing the batter. After each addition, mix the batter for about 15 seconds, or until everything is fully incorporated. Scrape the bowl a couple of times with a silicone spatula to make sure everything is mixed nicely.
Scrape the batter into the prepared pan, level the top with an offset spatula and bake until a skewer inserted into the middle comes out mostly clean, 45 to 55 minutes. (It’s best to check the cake after 40 minutes and then adjust the baking time accordingly, because ovens can vary.)
Remove the cake from the oven and allow it to cool in the pan for 15 minutes before carefully inverting it onto a wire rack to cool completely.