To make the pickled shallots, place all the ingredients into a small ceramic (non-reactive) bowl. Add 2 tablespoons of water and toss to combine. Set aside. The pickles can be made ahead of time and stored in a glass jar until ready to use. They will keep for several months in the fridge.
Preheat oven to 220˚C / 450˚F.
Place the cumin, coriander, turmeric, garlic powder, cinnamon, cayenne or chili powder in a large bowl and toss to combine. Add 2-3 tablespoon of olive oil and stir. Add the cauliflower and toss well until the cauliflower is coated in the spice mix.
Transfer the cauliflower to a baking sheet and arrange in a single layer. Season well with salt and pepper and place into the oven. Roast until the cauliflower is tender and golden around the edges, about 18-20 minutes.
Meanwhile, place the yoghurt, chives and za’atar in a bowl and stir to combine. Add about 1 tablespoon of olive oil and season with salt and pepper. Stir until combined.
On a large serving plate, spread 3/4 of the yoghurt. Top with the cauliflower, and drop dollops of the remaining yoghurt on top. Finish with a few pickled shallots and the chives. Serve alone or with flatbread, at room temperature.