Preheat oven to 375°F and line two baking sheets with parchment paper.
Add the diced pineapple and pineapple juice to a small, microwave-safe bowl and microwave on high for about 1 minutes. Stir and set aside to cool.
In a large bowl or the bowl of a stand mixer, add the butter, brown sugar, coconut milk powder, lime oil (or pineapple flavor), baking powder and salt. Beat together until light and fluffy, scraping down the bowl as needed.
Add the egg and beat until smooth.
Add in the flour, microwaved pineapple and any juice and toasted coconut and mix until thoroughly combined.
Drop the dough (approximately tablespoon size—a small cookie scoop is great for this) onto the baking sheets.
Bake for about 12–14 minutes, turning the pans and switching racks to ensure even baking, until the cookies are lightly browned on the bottom.
Cool the cookies in the pans for about 5 minutes, then transfer to a wire rack to cool completely.
To make the glaze, sift together the confectioners' sugar and coconut milk powder, then whisk in the juice and lime oil (if using) until smooth. The glaze should be thick but pourable. Add a little extra juice if needed.
Drizzle or pipe the glaze over the cookies, then top with a little toasted coconut and set aside to let the glaze harden.