Turn the oven to 210° C, air fun, with the rack set in the middle.
Take an oven proof baking sheet and add the cauliflower florets. Drizzle with 2 tbsp of olive oil, sprinkle the sumac and the pinch of salt and roast for 15 minutes. Remove from the oven and keep aside in a large mixing bowl.
In a large pot over medium heat add the remaining 2 tbsp of the olive oil and a minute later, and once heated, add the pearl couscous pasta along with the turmeric. Toss for a minute or two until well coated with the oil and slightly toasted. Add the water, increase the heat and bring to a boil. Then simmer with the lid covered for about 10 minutes, or according to package instructions, and until tender but not very soft. Remove from the heat to a colander and place under running water to stop the cooking. Allow to drain for about 10 minutes and add to the bowl with the cauliflower.
In the meantime, prepare the dressing by combining in a glass bowl all the ingredients and whisking until emulsified.
Then add to the couscous the shredded carrots, dry fruits and the preserved lemons, pour the dressing and stir to combine. Add the cilantro and gently toss and refrigerate if not using immediately. The flavors will really come together if refrigerated for few hours or even overnight. Serve in a deep dish and garnish with the chillie threads.