Preheat the oven to 200°C/fan 180°C/gas mark 6. Mix together all the marinade ingredients. Put the cauliflower in a large bowl and drizzle over the marinade. Stir well to make sure the cauliflower is well coated. Transfer to a roasting tin, making sure not to overcrowd the tin. Roast in the oven for 35-40 minutes, or until the cauliflower is soft and starting to caramelise. Remove from the oven and set aside.
Warm the tortillas in the oven for a couple of minutes, making sure they remain soft. Meanwhile, mix together the yogurt and half the herbs. Season with black pepper.
Divide the cauliflower between the four tortillas, then scatter over the onion and drizzle with the herb yogurt. Finish with the rest of the herbs, the pisatchios and the pomegranate.