To assemble you say take some of the cupcake out and fill with coconut filling, for which a recipe or any mention of hasn't been provided. (spoonfulofflavor.com)
This question came up because the amount of coconut filling / layer produced is minimal, giving a very thin layer of it. (forestandfauna.com)
These had a creamy coconut filling, and were very delicious. (bewitchingkitchen.com)