Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions.
Meanwhile, heat the olive oil in a large skillet over medium heat. Add the onion and bacon and cook until the onion is softened and the bacon is golden brown, about 10 minutes.
Add the diced tomatoes and simmer until the sauce is thickened, about 10 minutes.
Drain the spaghetti and add to the sauce. Toss to coat and season with salt and pepper.
Serve the spaghetti topped with the grated Pecorino Romano cheese.
Interesting Facts
The name "Amatriciana" comes from the town of Amatrice in Lazio, Italy where it is believed the dish originated.
The traditional recipe calls for guanciale, an Italian cured pork made from the pig's cheeks. Bacon is a common substitute.
Pecorino Romano cheese is a hard cheese made from sheep's milk.