In a large bowl combine the lemon zest, curry, turmeric, garlic powder, sumac and olive oil. Whisk together until combined. Line a large rimmed baking sheet with foil and spray with nonstick spray.
Add the cauliflower to the bowl and use a wooden spoon to try to get all the spices onto the cauliflower. Pour it onto the prepared pan.
Roast in the oven for 30-40 minutes. Toss the cauliflower and rotate the pan at least once to ensure even toasting.
Once roasted, season salt and pepper to taste, sprinkle with chopped parsley and serve.