In a blender, combine the chopped cucumbers, avocado, Greek yogurt, vegetable broth, lemon juice, garlic, salt, and black pepper. Blend until smooth and creamy.
Add the fresh dill and olive oil to the blender and pulse a few times to combine. Taste and adjust seasoning if necessary.
Transfer the soup to a large bowl or container, cover, and refrigerate for at least 1 hour to allow the flavors to meld and the soup to chill.
Before serving, stir the soup well. Ladle into bowls and garnish with chopped green onions.