Preheat the oven to 200°C. While the oven heats, make the dressing by combining the vinegar, oil and spices in a large bowl. Season to taste and set aside.
Chop the cauliflower into florets, place on a baking tray, drizzle with olive oil, season with salt and pepper, and roast for 25–35 minutes until golden brown and cooked through. Transfer to the bowl with the dressing.
Reduce the oven temperature to 180°C and toast the hazelnuts on a baking tray for 10 minutes until golden and the skins rub off easily. Transfer the nuts to a clean tea towel or paper towel. Fold the tea towel over and rub the skins away. Transfer the skinless, toasted nuts to a board, and roughly chop. Add to the cauliflower, along with celery and hazelnuts, toss and season to taste.
Serve between two for a large salad plate, or four as a small starter/accompaniment.