Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally, until tender yet firm to the bite, about 12 minutes. Drain.

Heat olive oil in a large skillet over medium heat. Add guanciale; cook and stir until sizzling, about 5 minutes. Add onion and chile pepper; cook and stir until softened, about 10 minutes. Stir in tomatoes; simmer until tomatoes break down into a sauce, about 20 minutes.

Stir spaghetti into the tomato sauce until well combined. Sprinkle generous amounts of pecorino Romano cheese over each serving.