Preheat the oven to 350 degrees F.
Parboil the carrots in boiling, salted water for 10 minutes, until they are very nearly cooked, then drain and put them into a roasting pan. You should flavor them while they're steaming hot, so while the carrots are cooking get a pestle and mortar and smash up the cumin seeds, chilles, salt and pepper. Add the garlic and thyme leaves and smash up again until you have a kind of paste. The idea here is to build up the flavors. Add enough extra-virgin olive oil to generously cover the paste, and a good swig of vinegar. This will be like a marinade, a rub and a dressing all in one! Stir together, then pour over the carrots in the pan, coating them well. Add the orange and lemon halves, cut side down.
These will roast along with the carrots, and their juice can be used as the basis of the dressing. Place in the preheated oven for 25 to 30 minutes, or until golden.
While the carrots are roasting, halve and peel the avocados, discarding the pits, then cut them into wedges lengthwise and place in a big bowl. Remove the carrots from the oven and add them to the avocados. Carefully, using some tongs, squeeze the roasted orange and lemon juice into a bowl and add the same amount of extra-virgin olive oil and a little swig of red wine vinegar. Season, and pour this dressing over the carrots and avocados. Mix together, have a taste and correct the seasoning. Call your gang round the table while you toast or broil your ciabatta slices.
Tear the toasted bread into little pieces and add to the dressed carrot and avocado. Mix together, toss in the salad leaves and cress and transfer to a big platter or divide between individual plates. Spoon over a nice dollop of sour cream, sprinkle over your toasted seeds and drizzle over some extra-virgin olive oil.
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Recipe Excerpted from JAMIE AT HOME by Jamie Oliver. Copyright (c) 2008. Published in the U.S. by Hyperion. All Rights Reserved. www.jamieoliver.com