Step 1: Cook the pasta. Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook according to package directions until al dente (firm to the bite). Do not overcook.
Step 2: Rinse and cool pasta. Immediately drain the cooked pasta in a colander. Rinse thoroughly under cold running water until the pasta is completely cool. This stops the cooking process and prevents sticking. Let it drain very well.
Step 3: Prepare vegetables and cheese. While the pasta cooks and cools, dice the bell peppers, halve the cherry tomatoes, thinly slice the red onion, halve the mozzarella balls, and slice the olives (if using).
Step 4: Combine ingredients. In a large mixing bowl, combine the cooled pasta, diced bell peppers, halved cherry tomatoes, sliced red onion, mozzarella balls, and sliced black olives (if using).
Step 5: Dress the salad. Pour about ¾ of the Italian dressing over the pasta and vegetables. Toss gently but thoroughly to ensure all ingredients are evenly coated. Add chopped fresh parsley if desired.
Step 6: Chill and serve. Cover the bowl and refrigerate for at least 30 minutes, or ideally 2-4 hours, to allow the flavors to meld. Before serving, give the salad another toss and add more dressing if needed, tasting and adjusting salt and pepper to your preference.