Preheat the oven to 200°C fan.
Coarsely grate a third of the cauliflower and set aside in a bowl.
Break the remaining cauliflower into florets, roughly 3cm wide, and add these to a separate bowl with the cauliflower leaves, if you have any, and onion.
Toss everything together with 2 tablespoons of oil and ¼ teaspoon of salt, then spread out on a large parchment-lined baking tray.
Roast for about 20 minutes, until cooked through and golden-brown.
Remove from the oven and set aside to cool.
Once cool, put the roasted vegetables into a large bowl with the 50ml oil, the grated cauliflower and the remaining ingredients, along with ¼ teaspoon of salt.
Toss gently, just to combine, then transfer to a platter and serve.