Cut the head off each octopus, just below the eyes, and discard. Cut each octopus in half and discard the hard little beak inside. Clean well and pat dry.
Bring a large pot of water to the boil and cook octopus for 1 minute. Drain well. Mix octopus, tomato, red pepper and onion.
Whisk together olive oil, vinegar, water, salt and pepper in a small bowl and pour over octopus. Refr