Bring a large pot of salted water to a boil. Cook the spaghetti according to the package instructions; reserve some cooking water and drain; set aside.
Heat a large skillet over medium high heat. Add oil, onion, garlic and pancetta. Cook until the pancetta gets brown and crispy, 3-4 minutes.
In a bowl, whisk eggs with cheese; season with salt and pepper to taste.
Add some of the cooking water to the hot pancetta skillet. Toss to coat the pasta with the oil. Remove skillet from heat and pour over egg mixture, tossing quickly so the eggs don't scramble. Add more of the hot cooking water to thin it out and form a sauce. Toss in parsley. Serve immediately with extra cheese. Serves 5.
Approximate Nutrient Analysis per serving (not including salt to taste):
620 calories, 24 g fat, 8 g saturated fat, 180 mg cholesterol, 900 mg sodium, 70 g carbohydrate, 4 g fiber, 2 g sugar, 27 g protein