Bring a large pot of salted water to a rolling boil. Add the rotini pasta and cook according to package instructions, usually about 8-10 minutes, until al dente. Drain and rinse under cold water.

In a spacious mixing bowl, combine the cooled rotini with sliced pepperoni, diced mozzarella, halved cherry tomatoes, black olives, chopped green bell pepper, and finely diced red onion. Toss gently for even flavor distribution.

Pour the Italian dressing over the mixture and toss gently until everything is coated.

Sprinkle in the dried oregano and season with salt and pepper. Mix gently to distribute seasonings.

Cover the bowl and refrigerate for at least 1 hour to chill and blend the flavors.

Before serving, toss the salad to redistribute the dressing and adjust seasoning if needed. Serve in a lovely bowl or individual portions.