Tri-Color Italian Rotini Pasta Salad

package of tri-color rotini pasta

of a medium red onion , chopped

stalk of celery , chopped

of a medium green bell pepper , chopped

of a medium red bell pepper , chopped

medium pitted black olives , sliced

commercial or homemade Italian dressing

tomato, seeded and chopped

Parmesan cheese , to garnish

Crumbled bacon , to garnish, optional