Bring a large pot of salted water to a boil and cook the spaghetti according to package instructions until al dente.
While the pasta is cooking, heat a large skillet over medium-high heat.
Add the guanciale to the skillet and cook until crispy and browned, about 5-7 minutes.
Reserve some of the pasta cooking water and drain the spaghetti.
Add the cooked spaghetti to the skillet with the guanciale and toss to combine.
Add a few tablespoons of the reserved pasta cooking water to the skillet to help create a sauce.
Remove the skillet from heat and add the grated Pecorino Romano cheese, black pepper, and a pinch of salt.
Toss the spaghetti and sauce together until the cheese has melted and the sauce is well combined.
Serve the spaghetti alla Gricia hot, garnished with additional grated Pecorino Romano cheese and black pepper, if desired.