Preheat your oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper.
In a large bowl, mash the overripe bananas until smooth.
Add coconut milk, vanilla extract, and brown sugar to the bananas. Stir until combined.
In another bowl, sift together flour, baking powder, nutmeg, and cinnamon.
Slowly fold the dry ingredients into the banana mixture. Be careful not to overmix.
Stir in grated coconut and, if desired, chopped walnuts or raisins.
Pour the batter into the prepared loaf pan, spreading it out evenly.
Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.