Preheat oven to 200°C (180°C fan-forced) and line 2 large baking trays with baking paper.
Place prepared sweet potato in a large mixing bowl, drizzle with 1 tablespoon olive oil and season well with salt and pepper. Toss until well coated and place on a prepared baking tray. Repeat process with the cauliflower florets.
Place cauliflower in the oven on the top shelf and the sweet potato on the middle shelf and roast for 30 minutes. Turn the vegetables over on each baking tray, swapping the sweet potatoes to the top shelf and the cauliflower to the middle shelf. Roast for a further 45 minutes or until vegetables are golden. Remove from oven and allow to cool.
For the dressing, combine yogurt, tahini, garlic, lemon juice, salt and pepper together in a small mixing bowl with 2 tablespoons of water, whisking to combine.
To serve, place roasted vegetables, chickpeas, mint, pomegranate seeds and spring onions together in a large mixing bowl, tossing to combine. Spoon onto a serving platter and drizzle with tahini dressing.