Fill a large pot with water, add a generous amount of salt, and bring it to a boil. Once boiling, cook the spaghetti according to package instructions until al dente. Reserve 1 cup of the pasta cooking water, then drain the spaghetti.
While the pasta is cooking, in a large bowl, whisk together the eggs, grated Pecorino Romano cheese, and a generous amount of black pepper until smooth and well combined.
In a large skillet over medium heat, add the diced pancetta and cook until crispy, about 4-5 minutes. Add the minced garlic and cook for an additional minute until fragrant. Remove from heat and set aside.
Once the spaghetti is done, quickly add the hot pasta to the skillet with the pancetta and garlic. Toss to combine, allowing the residual heat to warm the pasta and fat from the pancetta.
Remove the skillet from the heat, then quickly pour in the egg and cheese mixture, tossing continuously to create a creamy sauce. The heat from the pasta and pancetta will gently cook the eggs without scrambling them.
If the sauce seems too thick, gradually add some reserved pasta water until you reach your desired creaminess.
Taste and adjust with additional black pepper if desired.
Serve immediately, garnished with chopped parsley and extra cheese if you like.