Bring a saucepan of water to the boil, add the lentils and simmer for 20 minutes until just tender. Drain into a sieve, rinse and drain again and set aside. Wash and dry the pan.
Heat the oil in the cleaned pan then add the leek, pancetta and garlic and fry for 5 minutes, stirring until the pancetta is just beginning to turn golden. Add the Pernod and, when bubbling, flame with a long taper and quickly stand well back. As soon as the flames subside pour in the stock. Add the lemon rind and a little salt and pepper, then bring to the boil and simmer uncovered for 10 minutes.
Stir in the cooked lentils, cream and parsley, then taste and adjust the seasoning if needed. Heat the butter in a frying pan. Rinse the scallops in cold water and drain well, then add to the pan and fry for 3–4 minutes, turning until golden and cooked through.
Ladle the soup into shallow bowls and spoon the scallops into a small mound in the centre.