2) Meanwhile, combine the onions, garlic, tomatoes, Parmesan, basil, olive oil, salt and pepper in a food processor. Pulse just until the tomatoes are coarsely chopped (do not puree).
3) Drain the pasta, reserving some of the pasta water. Toss the pasta with the tomato mixture and fresh mozzarella in a large bowl. Add some of the reserved pasta water (about 60ml) if the sauce looks dry. Serve immediately.