Heat up the EVOO in a large pan and sauté the onion and garlic for 4 minutes.
Mix in the chicken stock and raise to a boil. Simmer for 5 minutes.
Add in the cucumber chunks to the pan and cook for another 3 minutes.
Add the watercress in and let it wilt. Pour it all into a food processor and blend until fully smooth.
Fill a small pan with water and bring to a boil. Steam the green beand for 4 minutes or until tender.
Add to the soup, season and warm through.