Heat the olive oil in a large skillet over medium heat. Add the guanciale strips and cook for about 5 minutes, turning occasionally, until golden and crispy. Remove the guanciale and set aside, leaving the rendered fat in the pan.

Add the crumbled chili pepper to the pan and cook for 30 seconds. Crush the San Marzano tomatoes by hand and add them to the skillet with their juices. Season with salt and pepper. Simmer on medium heat for 10 to 12 minutes, stirring occasionally, until the sauce thickens slightly.

Meanwhile, cook the bucatini in a large pot of salted boiling water until al dente. Reserve 1/2 cup pasta water and drain.

Return the guanciale to the sauce. Add the pasta and toss over medium heat, adding splashes of pasta water until the sauce clings to the pasta. Remove from heat, toss in most of the Pecorino Romano, and serve immediately with remaining cheese on top.