Blanch all the lettuce leaves together in lightly salted boiling water for about 3 minutes. Drain, reserving the water. Tip the lettuce leaves into a colander and leave to drain. Heat the oil in a heavy-bottomed saucepan and fry the onion and herbs together for about 6 minutes. Chop the drained lettuce leaves and add to the fried onion and herbs. Stir carefully, then add the reserved water. Stir, then bring to the boil, reduce the heat and simmer for about 20 minutes. Season with salt and pepper. Arrange the bread in a large, wide, warmed serving bowl and pour the soup over the bread. Serve at once.