1.Preheat oven to 170°C (150°C fan-forced). Grease 26cm x 32cm Swiss roll pan; line base and two long sides with baking paper.
2.Combine oats, flour, sugar and coconut in large bowl.
3.Combine butter, golden syrup and the water in medium saucepan; stir mixture with a wooden spoon until butter is melted.
4.Remove pan from heat. Add soda to the butter mixture (it will froth and bubble).
5.Pour butter mixture into oat mixture and stir with a wooden spoon until all the ingredients are mixed together. Spoon mixture evenly into pan, then press down on the slice with your hands until it is flat.
6.Bake, uncovered, about 30 minutes (it should feel firm when you touch it).
7.Stand slice in pan about 15 minutes. Turn slice out of pan, remove baking paper, then cut slice into pieces while still warm.
To make a slightly different variation of this slice, try adding ¾ cup dark chocolate chips, ¾ cup sultanas, or ¾ cup finely chopped dried apricots in with the oats (step 2). This recipe is a great lunchbox treat. It will keep in an airtight container for up to 4 days, so you can make it on the weekend to take to school.