Meanwhile, in a large bowl, toss the carrots, 2 tablespoons of the olive oil, and the coriander and cumin seeds. Squeeze the orange and lemon over the carrots, then add the squeezed fruit to the bowl, too. Season generously with salt and pepper and toss to mix. Spread on two large rimmed baking sheets and roast for about 25 minutes, until lightly charred and tender. Let cool; discard the orange and lemon.