Finely chop about one-third of one cucumber and set it aside for garnish.
Roughly chop the remaining cucumbers.
Add the chopped cucumbers, Greek yogurt, juice of one lime, tarragon, most of the mint leaves, and most of the chives to a blender.
Blend until completely smooth and creamy.
Taste the Cucumber Soup and add the juice from the second lime if you'd like a brighter, tangier flavor.
Pour into serving bowls or small glasses.
Top with the reserved diced cucumber, remaining mint, and chives.
Finish with a light drizzle of rapeseed oil and serve immediately, or chill for 30–60 minutes for an even cooler soup.