Heat the oil in a large, heavy-based saucepan over low-medium heat. Add the onion, and saute until softened. Increase the heat to medium, add the peppers. Cook, stirring occassionally, for 5 minutes. Add tomatoes and basil leaves, and toss to combine. Season with salt and pepper. Cover. Cook for further 8-10 minutes, mixing constantly until softened.
Cook the pasta in plenty of boiling salted water until it is al dente. Drain, pour-in the pasta into the serving bowl with the dressing/sauce mixture, mix in the parmesan and toss well.
Add mozzarella cubes and toss to combine. Serve hot.
