Place the onion in a colander over the sink and pour over a kettleful of just boiled water. Place the vinegar, sugar and salt in a small non-reactive bowl and whisk together until dissolved, then add the drained red onion. Stir well, making sure that the onion is completely submerged in the vinegar mixture. Leave for at least 30 minutes, or overnight, until the onion has turned a vibrant pink colour and softened slightly.
Preheat the oven to 220°C/gas mark 7. Heat the oil in a medium saucepan and cook the onion for 8-10 minutes until softened. Add the garlic clove with the ground spices and chilli and cook for 1 minute. Add the rinsed quinoa with 400ml water, then add the cardamom pods and cloves. Season and bring to the boil with a lid on, then turn down the heat and simmer for 15-20 minutes until the water is absorbed. Set aside to steam.
Meanwhile, mix all the spices for the cauliflower with the oil. Place the cauliflower on a large roasting tray making sure it is spaced out well. Pour over the spice mixture and toss so that it's evenly coating the cauliflower. Season and roast for 15 minutes – it should still be slightly firm when inserted with a skewer.
Meanwhile, combine the ingredients for the tahini drizzle in a small bowl. Add 3-4 tbsp warm water until it reaches a nice drizzling consistency.
To serve, divide the quinoa between 4 bowls. Top this with the cauliflower and rocket, then drizzle with the tahini dressing and divide the red onion between the bowls.