Bring a large pot of water to a boil, salt generously.
Put the bucantini in the water to cook. Do not break the pasta. Stir occasionally.
In a large pan, over medium heat add in a little olive oil if using pancetta, start cooking until the fat renders and it begins to brown. Add in a little ground pepper. .
About halfway until the pancetta is done, add in your red onion. Cook for a couple minutes, then add in your pureed tomatoes. Cook for a minute or two and taste and add salt and pepper as needed.
When the pasta is almost done to al dente, remove and add to the sauce to let finish cooking. Reserve the pasta water and add a little in to loosen the sauce if need be. Taste for seasoning. Add in your pecorino romano cheese. When the pasta is al dente the dish is finish.
If you would like to add arugula, toss the pasta with it at this point. Serve immediately with extra pecorino romano.
