Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a large bowl, combine the cauliflower, carrots, cumin, paprika, salt, pepper and olive oil. Toss until well-coated.
Spread the vegetables on the baking sheet in a single layer and roast for 20-25 minutes, until the carrots are tender.
Make the dressing: In a medium bowl, whisk together the tahini, garlic, lemon juice, and water. While whisking, slowly drizzle in the olive oil until the dressing is emulsified. Season with salt and pepper.
In a large bowl, mix together the onion and parsley. Add the roasted cauliflower and carrots, and toss well.