Peel the cucumbers, cut them in half lengthwise, and remove the seeds. Chop the cucumbers coarsely and place them in a blender with the lime juice, cilantro, buttermilk, and 8 ounces of the goat cheese. Blend until smooth. Add zest and season with salt and pepper.
Chill well before serving, or add ice cubes to blender if serving immediately.
Garnish with chunks of the remaining 2 ounces of fresh chèvre and a sprig of cilantro.