Step 1Heat the oven to 350 degrees. Parboil the carrots in boiling salted water for 10 minutes, until they are nearly cooked, then drain and place them in a roasting pan.
Step 2Meanwhile, in a mortar and pestle, smash the cumin seeds, chiles, one-fourth teaspoon salt and one-eighth teaspoon pepper. Add the garlic and thyme and smash again until you have a kind of paste. Add 1 1/2 tablespoons olive oil, or enough to generously cover the paste, and 1 teaspoon of vinegar. Stir together, then pour over the carrots, coating them well.
Step 3Add the orange and lemon halves, cut-side down, to the pan of carrots. Place in the oven for 25 to 30 minutes, or until the carrots are light golden brown
Step 4While the carrots are roasting, halve and peel the avocados, discarding the pits, then cut them into wedges lengthwise and place in a big bowl.
Step 5Remove the carrots from the oven and add them to the avocados. Using tongs, carefully squeeze the juice from the roasted orange and lemon into a bowl (you should have about one-half cup juice) and add the same amount of olive oil and 2 tablespoons vinegar, or to taste. Season with one-fourth teaspoon salt and one-eighth teaspoon pepper, or to taste, and pour enough dressing over the carrots and avocados to coat. Mix together, taste and correct the seasoning.
Step 6Toast, broil or grill the bread, then tear it into little pieces and add to the dressed carrots and avocados. Mix together, toss in the salad leaves and the watercress, add additional dressing to taste, and transfer to a big platter or divide among individual plates. You may not use all of the dressing; we used three-fourths cup.
Step 7Add a dollop of sour cream, if desired, sprinkle with toasted seeds and drizzle with more olive oil. Serve immediately.