Nopales are the paddles of various species of prickly pear cacti. They are sold in Mexican markets and increasingly in supermarkets, either precleaned and diced or in the form of paddles (almost always with the spines already removed). To prepare paddles, cut off any nubby parts with a vegetable peeler or sharp paring knife, then rinse well and dice. It is not necessary to peel off the outer skin.
Combine all ingredients in the bowl of a blender or food processor and blend until smooth. Strain into a pitcher.