Grease and line a lamington tin, then put to the side.
Place sweetened condensed milk and butter in a small saucepan; stir over low heat until smooth, then set aside.
In a large bowl combine biscuits, coconut and lemon rind. Add the warm butter mixture and mix until combined. Press the mixture into the prepared tin and refrigerate for 1 hour.
To make lemon icing, combine icing sugar and lemon juice in a bowl. Mix until smooth and spread over the base with a sprinkle of coconut. Refrigerate until icing is set and cut into small squares before serving.