Preheat the oven to 160 Celsius (320 Fahrenheit) and line a baking tray with parchment paper.
Place the oats into a food processor and process until finely ground. Set aside while you make the cookies.
Cream the butter and sugar in the bowl of an electric mixer fitted with a paddle attachment until smooth and creamy. Switch the mixer to it's lowest speed and add the golden syrup, flour, coconut, oats and mix until combined.
Using a teaspoon form balls of the dough and place on the baking tray, lightly flattening each one. Repeat for the remainder of the cookie dough.
Bake for 15 minutes, or until the cookies are golden before removing from the oven. Leave to rest on the tray for 5 minutes before placing on a wire rack to cool completely.
For the milk chocolate filling half fill a small saucepan with water and place over a medium low heat. Place the chocolate in a heat proof bowl (a glass bowl is ideal) and ensure the bowl does not touch the water. Leave the chocolate to slowly melt, stirring occassionally. When the chocolate has melted set aside to allow it to thicken to a spreading consistency. Take a cookie and turn it over to the flat side. Spread the chocolate on the cookie and sandwich with another cookie. Repeat with the remaining cookies.
For the chocolate icing filling, sift the icing sugar and cocoa into a bowl. Add the softened butter and stir to combine before adding the boiling water, little by little, until you have a spreadable consistency. Take a cookie and turn it over to the flat side. Spread the icing on the cookie and sandwich with another cookie. Repeat with the remaining cookies.