Place the walnuts, and garlic in the bowl of a food processor fitted with a steel blade, and process for about 15 seconds.
Add in the basil leaves, salt, and pepper. With the processor running, slowly pour in the olive oil to the bowl through the feed tube and process until the pesto is thoroughly pureed.
Add the grated Parmesan cheese and puree for a minute.
Prepare the pasta to the directions on the box. If you are in a rush, slightly over cook the pasta, and when it’s draining in the sink run cold water on it. This will stop the cooking process and cool the pasta down.
Meanwhile, chop up the tomatoes and the mozzarella, and set them aside.
In a large bowl, combine the pasta, pesto, tomatoes and mozzarella. Combine well and check for seasoning. Add in any salt and pepper as needed.