Begin by boiling a large pot of salted water over high heat. Once boiling, add the rotini pasta and cook until al dente, about 8-10 minutes. Drain and rinse under cold water.

Prepare your vegetables and toppings. Dice the mozzarella, chop the red onions, slice the bell pepper, halve the cherry tomatoes, and slice the pepperoni.

In a large mixing bowl, combine the cooled rotini pasta, diced mozzarella, pepperoni, halved cherry tomatoes, sliced black olives, diced bell pepper, and finely chopped red onion. Toss gently.

Drizzle the Italian dressing over the salad. Toss everything together until well coated.

Sprinkle dried oregano, salt, and pepper over the salad. Toss again and adjust seasoning to taste.

Cover and refrigerate for at least one hour to allow flavors to meld.

Serve chilled, giving the salad a gentle toss to redistribute the dressing before serving.