Bring a large pot of salted water to a boil and cook the spaghetti until al dente.
While pasta cooks, dice the chicken breast and pancetta into small, uniform pieces.
In a medium skillet over medium heat, sauté the pancetta until the fat renders and it becomes crispy.
Add the diced chicken to the skillet with the pancetta and cook until golden brown and cooked through.
In a small bowl, whisk together the egg, grated parmesan cheese, and black pepper until well combined.
Reserve 0.25 cup of pasta water, then drain the spaghetti.
Turn off the heat on the skillet and add the hot pasta, tossing with the chicken and pancetta.
Quickly pour in the egg mixture and a splash of pasta water, stirring constantly to create a creamy sauce without scrambling the eggs.
Serve immediately with an extra crack of black pepper.