Core, peel and dice the apples. Place them in a pot along with 1/4 cup of water. Cover and cook over low heat for 15-20 minutes, until soft.
Meanwhile, peel and de-seed the cucumber (optional if using an English Cucumber) and roughly dice it.
Once the apples have cooled a little, add them to a blender (or food processor) along with the cucumbers and your herb of choice. Blend until smooth. If you’re using a powerful blender, you shouldn’t need to add any extra liquid. If you do add extra liquid, add just a tiny bit at a time. Cucumbers are made of mostly water, so adding extra liquid will result in a watery puree.