Step 1Place bread in a shallow bowl, drizzle with red wine vinegar and set aside for 5 minutes to soften.
Step 2Roughly chop 1 1/2 cucumbers, reserve remaining half. Working in 2 batches, place soaked bread, tomatoes, capsicums, chopped cucumber, onion and 1 tablespoon of the oil in a blender, and blitz until completely smooth. Drain through a fine sieve into a large bowl, pressing as much of the liquid through the sieve as possible. Season soup to taste with cracked black pepper, then cover and refrigerate until chilled.
Step 3Finely dice remaining cucumber. Combine cucumber, remaining olive oil, chives and lemon zest in a small bowl.
Step 4Divide soup between 4 serving bowls. Top with a little of the cucumber mixture and serve.