In a blender, combine chopped cucumber with yogurt, lemon juice, red onion, garlic, dill, parsley, basil, and ¼ cup olive oil. Blend until smooth.
Season with sea salt and black pepper, cover, and refrigerate at least 8 hours or overnight.
Season soup again just before serving. Pour into bowls. Garnish with sliced cucumber, dill, and a drizzle of olive oil; and serve.
