Cook the rotini pasta according to package instructions until al dente. Drain and rinse under cold water to cool.
In a large mixing bowl, combine the cooled pasta, cherry tomatoes, cucumber, bell pepper, broccoli, and red onion.
In a separate bowl, whisk together the pesto sauce, mayonnaise, lemon juice, salt, and pepper until smooth.
Pour the dressing over the pasta and vegetables, and toss gently to coat everything evenly.
If using, sprinkle the grated Parmesan cheese over the top and mix lightly.
Cover and refrigerate for at least 30 minutes to allow the flavors to meld. Serve chilled.