Preheat your oven to 425°F. Line a baking sheet with parchment paper.
Place cauliflower florets in a bowl. Drizzle with 2 tbsp olive oil, and season with 1/4 tsp salt and 1/4 tsp pepper. Toss to coat the cauliflower evenly.
Spread the cauliflower evenly on the baking sheet. Place on the top rack of your oven and bake for 20 to 22 minutes or until the cauliflower is tender and golden brown, stirring halfway through.
While the cauliflower is roasting, prepare the celery, pistachios and parsley. Thinly slice the celery ribs and roughly chop the pistachios and parsley. Set aside.
Transfer the roasted cauliflower to a large bowl and let it cool for 20 minutes.
Add the sliced celery and chopped parsley to the bowl.
In a small bowl, combine the rest of the olive oil (2 tbsp), Sherry vinegar, 1/4 tsp salt and 1/4 tsp pepper, cinnamon and allspice.
Pour the dressing over the cauliflower bowl. Toss gently to combine.
Transfer the roasted cauliflower salad to a serving dish and sprinkle pistachios on top.
Enjoy immediately, or let it sit for a bit to allow the flavors to meld together. This salad can be served warm or at room temperature, making it a versatile addition to any meal.