Bring a large pot of salted water to a boil over high heat. Add rotini pasta and cook until al dente, about 8–10 minutes. Drain and rinse under cold water.

In a small bowl or jar, whisk together olive oil, red wine vinegar, Dijon mustard, garlic, oregano, salt, and pepper until emulsified.

In a large mixing bowl, combine cooled pasta, cherry tomatoes, cucumber, red bell pepper, red onion, black olives, mozzarella, and sun-dried tomatoes. Add pepperoni or salami if desired.

Pour dressing over the pasta mixture and gently toss to coat.

Cover and refrigerate for at least 30 minutes to allow flavors to meld.

Before serving, fold in fresh basil and serve chilled.