Cut the cauliflower into florets. Peel and quarter the onions. Spread the florets in a flat baking dish or on a tray, place onions between them. Pour some olive oil over it and season with salt. Mix everything. Roast in an oven preheated to 200 degrees for 30 minutes until brown. Turn the florets 2-3 times.
Meanwhile, quarter the olives, finely chop the capers and raisins and place in a salad bowl. Mix the olive oil, mustard and lemon juice and pour over it.
Put the hot, roasted cauliflower in the bowl, add the chopped herbs, mix everything well, season with salt and pepper.