Halve the melon and scoop the seeds out. Scoop the flesh out of the skin and add it to the blender. Peel the banana and break it into the blender.
Slice a 1cm-thick chunk off the ginger, peel it and grate it into the blender (you can add more ginger later if you prefer). Grate in the lime zest and squeeze in half of the juice.
Pour in 330ml oat drink and add a handful of ice cubes. Whizz till smooth, taste and grate in a little more ginger or add a squeeze more lime juice. Blend again, if necessary. Pour into a couple of glasses and serve.