1) To poach the seafood, you will need a large saucepan fitted with a colander insert. In the bottom of the pan, combine the celery, carrot, onion, bay leaf, lemon juice, salt and water. Bring to the boil.
2) Place the calamari in the colander and cook in the simmering water for 2 minutes. Remove from the water, transfer to a large bowl and set aside. Place the scallops in the colander and cook until opaque, about 3-4 minutes. Remove from the water and transfer to the bowl with the calamari (large sea scallops may be cut in half horizontally after cooking; bay scallops may be left whole). Place the prawns in the colander and cook until pink, about 3 minutes. Remove from the water. Peel, devein and cut in half horizontally, adding them to the bowl with the calamari and scallops.
3) Remove the colander from the pan and place the octopus directly in the saucepan, adding more water if necessary to completely cover. Bring to the boil. Reduce the heat and gently simmer until tender, about 40-50 minutes. Transfer the octopus to a bowl and rinse under cold running water until octopus is completely cooled, about 5 minutes. Use your fingers and a small paring knife to remove the outer skin. Discard the hard beak and head sac. Cut the tentacles and octopus on the bias into 2.5cm pieces and add to the bowl with the other seafood.
4) To prepare the salad, toss the julienned celery, carrots, peppers, spring onions, parsley, basil and garlic together in a serving bowl. Add the seafood and toss. Add the lemon juice, vinegar and olive oil and toss well. Season with the salt and generous grindings of pepper.
Arrange 45g of lettuce on each serving plate. Top with equal portions of the seafood and vegetable mixture, and serve immediately.
Variations: 6-8 steamed mussels may be added to the basic recipe and tossed with the other seafood. To extend the recipe and add a new texture dimension, 100g cubed, peeled and cooked potatoes and/or 100g cooked or tinned (drained and rinsed) cannellini beans may be added to the basic recipe. Although it isn't traditional, you can also add a hint of chopped coriander, about 2 teaspoons.