Bring a large pot of salted water to a rolling boil. Add 12 ounces of rotini pasta and cook according to package instructions, typically around 8-10 minutes, until al dente. Drain the pasta and rinse it under cold water to stop the cooking process. Allow it to cool completely, then set it aside in a bowl.

While the pasta cools, prepare the vegetables and dressing. Dice the red and green bell peppers, thinly slice the red onion, and chop the salami into bite-sized pieces. Slice the black olives. In a separate bowl, whisk together the Italian dressing, mayonnaise, and lemon juice until smooth and well combined.

In a large serving bowl, combine the cooled rotini pasta with all the prepared vegetables, diced salami, sliced olives, and fresh mozzarella pearls. Fold everything together, ensuring all ingredients are evenly distributed. Drizzle the creamy dressing over the salad and toss until all pasta is coated.

For the best flavor, allow the creamy Italian pasta salad to chill in the refrigerator for at least one hour before serving. If serving immediately, it's best enjoyed at room temperature.