Bring a large pot of salted water to a rolling boil over medium-high heat. Add the tri-color rotini pasta and cook according to the package instructions, typically 8-10 minutes, until al dente. Drain the pasta in a colander, then rinse it thoroughly with cold water to cool it down. Set the pasta aside to drain completely.

While the pasta is cooling, chop the cherry tomatoes, red onion, and green bell pepper into bite-sized pieces. Slice the pepperoni into thin rounds, adding a delicious zesty element. Gather all the vegetables and meats in a large mixing bowl.

Once the pasta has cooled, add it to the bowl with the chopped vegetables and sliced pepperoni. Gently fold in the mozzarella cheese and grated Parmesan cheese.

In a separate medium bowl, whisk together the olive oil, red wine vinegar, Italian seasoning, garlic powder, salt, pepper, and red pepper flakes. Mix well until the vinaigrette is smooth and well combined.

Pour the homemade vinaigrette over the pasta mixture in the large bowl. Toss the salad gently to coat all ingredients evenly with the dressing.

Cover the bowl with plastic wrap or a lid and refrigerate the pasta salad for at least one hour. This chilling time allows the flavors to meld beautifully.

Before serving, give the Classic Pasta Salad a good toss to redistribute the dressing. Serve this delightful salad cold or at room temperature.