Cook the rotini in a large pot of salted water according to the package directions for "al dente." It should be firm to the bite.
Drain the pasta and immediately rinse it under cold water. This stops the cooking and prevents the starch from making the salad gummy.
In a large mixing bowl, combine the cooled pasta, your 2 ½ cups of assorted vegetables, mozzarella pearls, and black olives.
Pour about ¾ of the bottle of Italian dressing over the mixture. Toss thoroughly until the spirals of the pasta are filled with dressing.
Let the salad sit in the fridge for at least 20 minutes to allow the flavors to meld. Right before serving, add the remaining dressing and a final crack of black pepper.