Pull thin zest of a lime from the peel. Squeeze the limes. Finely puree the peach pieces with the lime juice, sugar and ginger ale in a blender. Add 3 - 4 handfuls of crushed ice and mix briefly, then pour everything into a jug.
Fill the glasses 3/4 full with crushed ice and fill up with the slush. Sprinkle the zest on top and serve.