Julienne cut peppers and finely chop onions. Mince garlic.
In a pan, add oil and saute onions for 5 minutes. Add garlic, cooking for an additional 2 minutes. Add peppers, cooking for 6 more minutes.
Cook pasta in boiling water for one minute less than package instructions. Drain pasta, reserving half a cup of the cooking water. Mix pasta and vegetables together. Garnish with Parmesan and parsley.