Heat olive oil in a large skillet over medium heat; add guanciale. Cook, turning occasionally, until evenly browned and crispy (about 5 to 10 minutes). Remove from heat and drain on paper towels.

Bring a large pot of salted water to a boil. Cook spaghetti in the boiling water until tender yet firm to the bite, about 9 minutes. Drain and return to the pot. Let cool, stirring occasionally for about 5 minutes.

Whisk eggs, half of the Pecorino Romano cheese, and some black pepper in a bowl until smooth and creamy.

Pour egg mixture over the cooked pasta, stirring quickly until creamy and slightly cooled. Stir in guanciale.