Wash the rice really well, then leave to soak in cold water for 1 hr. Put the onion in a small bowl and toss with the lemon juice, the sugar and a pinch of salt. Leave to pickle while you make the pilaf.
Heat the oven to 200C/180C fan/gas 6. Whisk 2 tbsp harissa, the garlic and oil in a large bowl, then add the cauliflower and toss to coat in the sauce. Season, then tip into a roasting tin and roast for 30 mins until tender and golden.
Meanwhile, mix the saffron, bay leaves, stock and 2 tbsp harissa in a pan over a very low heat to keep warm while the cauli roasts.
Remove the cauli from the oven, tip into a dish and squeeze over the juice from one of the lemon wedges. Drain the rice and tip into the roasting tin. Pour over the infused stock, and mix well. Stir in the sultanas, half the almonds, the dill, chickpeas, and half the cauliflower. Cover the tin with a double layer of foil, sealing well, then bake for 30 mins until the rice is tender and stock is absorbed.
Fluff up the rice with a fork, then fold in the remaining cauliflower (this creates a contrast of cauli textures). Scatter over the extra dill, the remaining almonds, the pomegranate seeds, if using, the pickled red onions and remaining lemon wedges to squeeze over.