Cook the pasta according to the package directions. Drain and rinse well. Then return the pasta to the pot.
Meanwhile, make the pesto. Add the basil, pine nuts, and garlic to a food processor. Blend until finely minced. With the machine running, drizzle in the olive oil, until the mixture comes together. Add the parmesan and salt. Pulse to combine.
When the pasta is cooked, add the pesto, tomatoes, mozzarella, pine nuts, and arugula. Toss well to coat the pasta and soften the arugula. Serve.