Cook pasta according to package directions until al dente; rinse under cold water and drain. Let cool.
In a large bowl, combine the pasta, bell peppers, tomato, green onions, mushrooms, pepperoni, olives, garlic, oregano, salt and pepper. Toss together, then cover with plastic wrap and refrigerate until chilled.
Just before serving, mix in the dressing and the cheese. Toss well.
*If you refrigerate this salad with the dressing already added to it, you may wish to add additional dressing when you are serving it later. The pasta will tend to absorb the salad dressing.