Cold cucumber soup

Ingredients

• 2 large European cucumbers (2 1/4 pounds), halved and seeded—1/2 cup finely diced, the rest coarsely chopped


• 1 1/2 cups plain Greek yogurt


• 3 tablespoons fresh lemon juice


• 1 small shallot, chopped


• 1 garlic clove


• 1/3 cup loosely packed dill


• 1/4 cup loosely packed flat-leaf parsley leaves


• 2 tablespoons loosely packed tarragon leaves


• 1/4 cup olive oil, plus more for drizzling


• Salt


• Fresh ground white pepper


• 1/2 red onion, finely chopped