Preheat your oven to 325 degrees F. Spread 3/4 cup shredded coconut on a baking sheet in an even layer and toast for 4 to 6 minutes, stirring halfway, until golden. Set aside to cool. Increase the oven temperature to 350 degrees F.
In a medium bowl, whisk together gluten free all-purpose flour blend, baking powder, and salt. Stir in the toasted coconut.
In a large bowl, beat softened butter and granulated sugar with an electric mixer until light and fluffy, about 3 minutes. Beat in the egg, lime juice, lime zest, and vanilla extract until combined.
Add the flour mixture and mix on low speed until just combined into a soft dough. Line two baking sheets with parchment paper. Scoop rounded tablespoons of dough, roll into balls, and place 2 inches apart.
Bake for 11 to 13 minutes until the edges are just set and lightly golden. Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Whisk together powdered sugar and 2 tablespoons lime juice until smooth and pourable. Spoon or drizzle the glaze over each cooled cookie, then top with a sprinkle of additional toasted coconut and a pinch of lime zest. Let the glaze set for 15 minutes before serving.