Bring a large saucepan of salted water to a rolling boil.
Heat a large deep frying pan over medium heat and add the olive oil.
Add the cubed smoked pancetta and cook for 8–10 minutes, stirring occasionally, until crispy and fat is rendered.
Use a slotted spoon to transfer most of the pancetta to a plate, leaving the fat in the pan.
Add the chopped onion to the pan and sauté for 5–7 minutes until softened and translucent.
Stir in the crushed garlic and dried chilli flakes and cook for 1 minute until fragrant.
Pour in the chopped tomatoes, season with salt and black pepper, and bring to a gentle simmer.
Reduce heat to low and simmer the sauce for 15 minutes, stirring occasionally.
Meanwhile, add the bucatini to the boiling water and cook for 9–11 minutes until al dente.
Reserve 150 ml of pasta cooking water, then drain the bucatini.
Add the drained bucatini to the sauce along with most of the crispy pancetta and half the Pecorino Romano.
Pour in a splash of reserved pasta water and toss everything together until the sauce is silky and clings to the pasta.
Divide the pasta between plates and top with the remaining pancetta and extra Pecorino Romano, with a final grind of black pepper.
Serve immediately.