Preheat oven to 180 degrees celsius (160 if using fan forced).
Grease and line a standard sized slice tray (approximately 18 X 28cm) with baking paper.
Place the butter, golden syrup and brown sugar into the Thermomix bowl and cook for 3 minutes, 100 degrees, Speed 1.
Add the bicarbonate of soda to the melted butter mixture and combine mix for 10 seconds on Speed 3.
Scrape the sides of the bowl and add the rolled oats, plain flour and coconut. Mix for 12 seconds on Speed 3, Reverse.
Scrape down the sides of the bowl and mix for a further 5 seconds, Speed 3, Reverse.
Transfer the mixture to the prepared baking tray press down to flatten the surface.
Bake for approximately 22 - 25 minutes or until the top of the slice lightly golden brown.
Leave in the baking tray to cool for 10 minutes before transferring to a wire rack to cool completely.
When the slice has cooled completely, cut it into pieces.