1. In a large saucepan, bring water to a boil, and add pasta. Check the cooking time for the pasta, and add peas 5 minutes before the pasta will be done.
2. While pasta is cooking, heat olive oil in a large skillet. Add chopped onion and saute for 4 to 5 minutes, until soft. Add garlic and cook an additional 2 minutes. Set aside.
3. Drain cooked peas and pasta; add them to the skillet. Over medium heat, stir until pasta is mixed with onion and garlic. Remove from heat. Season with salt and parsley, and garnish with shaved Parmesan cheese, if desired. Serve immediately.