Bring a large saucepan of salt water to boil (about 1 teaspoon of salt) over medium-high heat. Once the water has come to a boil, add the pasta and cook according to the package directions until it is al dente. Drain pasta, reserving one cup of pasta water.
Cook the cubed guanciale in a large skillet over medium heat, stirring occasionally to ensure even cooking. Cook until crispy and the fat has been rendered, then remove it from the skillet using a slotted spoon.
Add the pepper to the skillet with the grease from the guanciale and cook it until it is toasted about 1 minute.
Add ½ cup of the pasta cooking water to the skillet with the toasted pepper, turn the heat to high, and reduce it by about half.
Turn off the heat and add the cooked pasta, guanciale, and most of the cheese - reserve a little cheese for topping. Stir vigorously to incorporate. Note: Add more pasta water if the sauce isn't silky and you see unmelted cheese.
Serve with additional ground black pepper and grated cheese.