In a large pan, add extra virgin olive oil and saute the garlic and onions over medium heat. Add salt and pepper and cook down for 5-10 minutes. Add half the chopped parsley and stir. Add the peas and a bit of hot pasta water. Stir well and turn heat to low.
Add cooked pasta and stir well with remaining parsley. Add some grated cheese and stir again, add a bit more extra virgin olive if necessary.
Recipe by Scordo.com - Italian Food Recipes and Lifestyle at http://www.scordo.com/pasta/penne-with-peas-onions-and-percorino-romano.html