1. Heat over to 425 degrees.
2. Quarter the carrots lengthwise and cut each length crosswise into 2-inch chunks. With a mortar and pestle or using the side of a knife, lightly crush the cumin, coriander and fennel. Spread carrots on a large rimmed baking sheet and toss with 2 tablespoons oil, crushed spices, 3/4 teaspoon salt and cayenne. Transfer to oven and roast, tossing occasionally, until carrots are tender and caramelized, 30 to 40 minutes. Cool to room temperature.
3. Meanwhile, grate zest of 1 orange into a small bowl. Whisk in garlic, remaining 1/4 teaspoon salt, and lemon juice. Whisk in 2 tablespoons oil.
4. Slice the tops and bottoms from each orange. Stand each orange on a flat surface and slice away the rind and pith, top to bottom, following curve of the fruit. Hold oranges over a large bowl and slice away fruit between the membranes, releasing segments into the bowl.
5. Toss carrots, arugula and olives into the bowl. Gently toss in dressing. Taste and add more salt and lemon juice if necessary.