Preheat the oven to 180°C. Line a flat baking tray with baking paper. In a large mixing bowl place all dry ingredients and stir until combined. Set aside.
In a smaller bowl whisk together the beaten egg, melted butter, honey, zest and juice of the mandarin. Pour the citrus egg mixture over the dry ingredients and quickly stir until evenly combined.
Tip the mixture into the prepared tray, taking care to press down on tray to form a rectangle with 1cm thickness and bake at 180C for 20 minutes or until golden brown.
Remove from oven and place on a wire rack. Allow to cool completely before removing from tray, then slice into bars. Store in an airtight container. Keeps for 1 week.