Put the tomatoes in a large pan or bowl and pour over enough boiling water to cover. Leave for about 1 minute, then drain, skin carefully and roughly chop the flesh.
Trim the green fronds from the fennel and discard. Finely slice the bulb and put it in a saucepan with 300 ml (½ pint) lightly salted boiling water. Cover and simmer for 10 minutes.
Meanwhile, crush the coriander seeds and peppercorns using a pestle and mortar. Gently heat the oil in a large pan and add the crushed spices, garlic and onion. Cook gently for 5 minutes.
Add the vinegar, lemon juice, tomatoes and oregano, reserving a few oregano leaves to garnish. Give the mixture a good stir and add the fennel along with the cooking liquid, tomato purée and salt. Bring to a simmer and leave to cook, uncovered, for 10 minutes.
Transfer the soup to a food processor or blender and process lightly. Cool and chill overnight and serve garnished with the reserved oregano leaves and green olives.