If you don't have a food processor you can coarsely grate the cauliflower instead. Chickpea pasta is one of the best and most delicious gluten-free alternatives to regular pasta, but if you wanted you could use whole wheat pasta instead.
In a food processor, blitz the cauliflower until it is riced and tip into a bowl. Add the mushrooms to the food processor and pulse these too until they are chopped small.
Heat the oil in a large saute pan and fry the onion for 5 minutes over a medium heat until soft, then add the garlic, chile flakes and rosemary and fry for 30 seconds. Add the cauliflower and mushrooms, season well with salt and pepper and fry over a high heat for 6 to 7 minutes. Add the tomato puree and cook for a few more minutes.
Meanwhile, cook the pasta in a saucepan of boiling salted water for 10 minutes. Drain, reserving 250ml (1 cup) of the water. Add the pasta to the cauliflower pan and toss together with half the Parmesan for 2 to 3 minutes, loosen with the reserved pasta cooking water as needed. Serve with the rest of the Parmesan scattered over the top.