Heat the oil in a large frying pan over a medium-high heat and tip in the cauliflower florets, stalks and leaves. Season, cover and fry for 8-10 mins, shaking the pan now and then, until lightly browned and softened. Stir the tomato purée and tomatoes, cover and cook for 5 mins more until the tomatoes have burst. Add the garlic, olives and harissa, and cook for 2-3 mins until fragrant.

Meanwhile, cook the pasta following pack instructions. Drain, reserving a mugful of the water. Stir the pasta and a splash of the water into the tomato mixture. Season, scatter over the parsley and serve.