Halve the avocado and scoop the flesh into your blender, discarding the stone. Finely grate the zest from the lime and slice off the white pith. Chop the flesh. Add the lime zest and flesh to the blender.
Chop the courgette into chunks and add to the blender with the walnut halves and a few ice cubes. Pour in the maple water. Blitz together till smooth, and serve.