Bring a large pot of salted water to a rolling boil. Add the tri-color rotini and cook according to package directions until al dente, about 10-12 minutes, stirring occasionally.
Drain the pasta in a colander and rinse thoroughly under cold running water until fully cooled. Shake off excess water and set aside.
Halve the cherry tomatoes, dice the green bell pepper, and finely dice the red onion. Drain the black olives well and slice the pepperoncini if using.
In a small bowl or jar with a tight-fitting lid, combine the extra virgin olive oil, red wine vinegar, Italian seasoning, garlic powder, salt, black pepper, and red pepper flakes if using. Whisk or shake vigorously until combined and slightly thickened.
Transfer the cooled pasta to a large mixing bowl. Add the cherry tomatoes, bell pepper, red onion, black olives, pepperoncini, mini pepperoni, mozzarella pearls, and parmesan cheese.
Pour about three-quarters of the dressing over the top and toss gently with salad tongs until evenly coated. Reserve the remaining dressing for later.
Cover the bowl and refrigerate for at least 30 minutes, or up to 24 hours, to allow the flavors to meld.
Just before serving, give the salad a final toss and pour in the reserved dressing. Taste and adjust salt, pepper, or red pepper flakes as needed. Serve cold, garnished with extra parmesan cheese if desired.