Cut prickly pears in half lengthwise and scoop out flesh with a spoon. Process in a blender until smooth. Push pulp through a fine mesh strainer to extract about 1 1/2 cups juice. Discard pulp.
Place prickly pear juice, water, lime juice, stevia, and mint in a blender. Blend until smooth. Pour into two 16-ounce glasses filled with ice.
