Peel the cucumber, cut into hald lengthwise and scrape out the seeds and roughly chopped and place in the blended. Peel and dice the avocados and add into the blender. Add in the 1 cup of the broth, cumin, juice and cilantro. Blend in high until pureed. Add in the remaining broth and blend until smooth. Add salt if desired. If necessary, add a little bit of water. Pour the soup into a bowl and cover with plastic wrap and refrigerate until chilled. Serve with mint and green onion if desired.