Pre-heat oven to 425 degrees and line 2 rimmed baking sheets with parchment paper.
Cut cauliflower into florets roughly 1 1/2 inches wide. Peel and slice carrots diagonally about 1/2 inch thick.
In large bowl, combine cauliflower with 1 1/2 tbsp. olive oil and 1 1/2 tsp. cumin seeds, and season with salt and pepper; toss to coat.
On prepared baking sheet, spread out cauliflower evenly. In large bowl, toss carrots with remaining 1 1/2 tbsp. olive oil and 1 1/2 tsp. cumin seeds, and salt and pepper. Transfer carrots to other prepared baking sheet.
Roast until vegetables are tender and brown, stirring vegetables and rotating baking sheets once to ensure even cooking, about 35 minutes.
In serving bowl, combine carrots and cauliflower and squeeze lime juice on top, to taste.