Heat olive oil in a small skillet over moderate heat. Add shallot, garlic, green onions, salt and pepper and sauté until fragrant. Remove from heat to cool

In a large blender, place cooled shallot mixture along with cucumber, vegetable stock, yogurt, lemon zest and juice, salt, pepper, mint and dill. Blend until smooth. (You may need to do this in batches in a smaller blender - it fit just right in my Vitamix). Taste for seasoning and adjust if necessary.

Pour soup into a large container. Cover and chill in the refrigerator until ready to serve.

To serve, spoon soup into 6 bowls and top each with a few drops of hot chili oil. Garnish with additional herbs and sliced cucumber, if desired.