Fry the squid very briefly (one to one and a half min) in a little olive oil. Season with salt and pepper and place in a suitable bowl.
Season crab tails and scallops with salt and pepper and steam briefly in a little olive oil together with olives and garlic – about one and a half min. Also in the baking dish form.
Steam the onion and mussels in a frying pan in a little olive oil and add to the squid and crab tails, together with the tomato pieces.
Make a salad dressing with salt, pepper, vinegar, sugar and the remaining oil and dress the lettuce with it. Sprinkle the coarsely chopped basil leaves on top and pull a little.
Garnish with lemon wedges and serve with crusty bread.