Cut the cauliflower into florets, put on a baking paper-lined baking tray and drizzle with 2 tbsp of the oil, Season with salt and roast for 20 minutes turning halfway, until golden.Meanwhile, cook the pasta according to the packet instructions, then drain reserving a ladleful of the cooking water.
Heat the remaining 2 tbsp oil in a frying pan over a medium heat. Finely chop and cook the shallots for 3 minutes, then add the garlic and chilli flakes and fry for a further 2 minutes.
Add the roasted cauliflower, pasta, reserved waterand lemon juice, then grate in the cheese. Mix well, then taste and season.
Coarsely chop the parsley, then sprinkle overthe pasta with the hazelnuts. Grate over extra Parmesan Cheese to serve.