Bring a large pot of salted water to a boil.
Cook the spaghetti according to the package instructions until al dente.
Reserve about 1 cup of pasta water, then drain the spaghetti and set aside.
In a large skillet, cook the diced pancetta or guanciale over medium heat until it is crispy and the fat has rendered. Remove from heat and set aside.
In a bowl, whisk together the eggs and grated Pecorino Romano cheese until well combined.
Add the minced garlic to the skillet with the cooked pancetta or guanciale and cook for about 1 minute until fragrant.
Add the cooked spaghetti to the skillet and toss to combine with the pancetta and garlic.
Remove the skillet from heat and pour the egg and cheese mixture over the spaghetti, tossing quickly to coat the pasta and prevent the eggs from scrambling. Add reserved pasta water as needed to create a creamy sauce.
Season with freshly ground black pepper and salt to taste.
Garnish with chopped fresh parsley if desired.
Enjoy your meal!