Preheat the oven to 220 °C. Line a baking tray with baking paper.
Spread the sweet potatoes, chickpeas and onion on the baking tray. Drizzle over the olive oil and mix. Sprinkle over the cumin, chilli flakes, salt and pepper. Mix again.
Roast in the middle of the oven until the chickpeas are crispy and the sweet potatoes tender, 25-30 minutes, giving it a stir halfway through if necessary.
Meanwhile, whisk together the yoghurt, tahini and lemon juice. Season to taste with salt and pepper.
Serve the chickpea traybake warm (but not hot), topped with the tahini yoghurt, herbs and pomegranate.
