If using whole spices: In a small sauté pan lightly toast the seeds and place in a spice grinder. Pulse until seeds are ground. Set aside, let cool, then mix with salt. Otherwise if using ground cumin, coriander, fennel, celery seeds (use 1/4 teaspoon each) and 1 tsp salt in a small bowl. Set aside.
In a large bowl toss the carrots with the olive oil and spices to coat.
On the parchment lined baking sheet, roasting pan or cast iron skillet, spread the seasoned carrots to a single layer.
Roast for 30 minutes, occasionally shaking the pan to turn and coat. You want these evenly roasted and slightly caramelized. Remove from oven and squeeze the lime all over. Sprinkle with chopped mint leaves. Serve warm.
Either use baby carrots, or if using large carrots, peel, slice and cut into uniform pieces for even roasting.