Peel the cucumbers and cut them lengthwise. Using a spoon, scoop out the seeds. Roughly chop the cucumbers into 1-inch chunks.
In a blender, combine the cucumber chunks, Greek yogurt, garlic, dill, mint, lemon juice, olive oil, salt, pepper, and cumin. Pulse a few times to break down the larger pieces.
Blend on high speed until smooth and creamy, about 1-2 minutes.
Taste and adjust seasonings as needed. Remember that cold temperatures mute flavors, so season slightly stronger than you'd prefer when served.
Transfer the soup to an airtight container and refrigerate for at least 2 hours, preferably overnight.
Before serving, stir the soup well. Pour into chilled bowls and garnish with a drizzle of olive oil, diced shallots, additional fresh dill, and toasted pine nuts if using.