Preheat the oven to 350°F. Grease a 9x5" loaf pan and set aside.
In a medium bowl, whisk the flour, baking powder, and salt together. Set aside.
Using a hand mixer or a stand mixer fitted with the paddle attachment, cream the butter with the sugar until smooth. Add the Greek yogurt and vanilla and beat to combine. Add the dry ingredients in thirds, alternating with the buttermilk and beating briefly after each addition to incorporate. Be sure to start and end with the dry ingredients. Beat until combined. Fold in the coconut.
Transfer the batter to the prepared baking pan. Bake for 60-65 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool in the pan for 15 minutes, then transfer to a wire cooling rack to cool completely.
To make the glaze, add the buttermilk to the powdered sugar, one tablespoon at a time, until desired consistency is achieved. Spread or drizzle over the cooled cake, then top with toasted coconut.
Notes
To toast the shredded coconut in the microwave, spread in a single layer in a microwave-safe dish. Microwave in 30 second intervals, removing and stirring after each interval, until coconut is toasted.