Place 2/3 cucumber, 1 1/2 avocado, yogurt, lime juice, scallions, salt, pepper, jalapeno, and 3 tablespoons cilantro in a blender or Vitamix. Puree until smooth. Thin out with water, a tablespoon at a time, until desired consistency is reached. (Note: I generally do not add water, but some people may prefer a thinner soup.)