Preheat your oven to 180°C (fan-forced) and line a slice tin (approx 28cm x 18cm) with baking paper. Make sure you leave paper hanging over the edges to help you remove it from the tin later.
In a large bowl, combine the flour, oats, sugar and coconut using a large metal spoon and make a well in the centre.
Place the butter and golden syrup in a small saucepan and cook over a low heat for 6 - 8 minutes or until the butter has melted and the ingredients have combined. Make sure to stir the mixture every minute or so.
In a separate bowl, combine the bicarbonate of soda and boiling water. Then remove the melted butter mixture from the heat and stir in the dissolved bicarbonate of soda mixture.
Pour the wet ingredients into the well made from the dry ingredients. Use a large metal spoon to combine.
Pour the slice into your prepared pan and using the back of a spoon, press the mixture evenly into slice tray. Bake for 25 minutes or until the slice is golden brown.
Carefully remove the slice from the oven and allow it to completely cool in the tray.
Use the overhanging baking paper to remove the slice from the tin and cut into squares to serve.