Preheat oven to 180C. Grease oven tray.
Whisk sugar, eggs, and lemon juice in medium bowl until combined. Stir in sifted flour and baking powder, coconut and rinds.
Knead dough on floured surface until smooth. Divide dough in half, roll each portion into a 20cm log. Place logs on tray and bake for 30 minutes. Cool on tray for 10 minutes.
Reduce oven temperature to 150C.
Using a serrated knife, cut logs diagonally into 8mm thick slices. Place slices, in a single layer, on ungreased oven trays. Bake biscotti for about 30 minutes or until dry and crisp, turning half way through baking. Cool on wire rack.