To a large pot of water, add salt and bring to a boil over high heat.
Add bucatini pasta and cook according to package direction until al dente.
Heat a large fry pan over medium heat. When hot, add olive oil and then diced guanciale. Saute for 4 minutes until the guanciale's fat renders out. The guanciale will start to turn golden and become crisp. Stir frequently.
Add the onion and saute until translucent, about 3 minutes.
Add garlic and cook for 2 minutes.
Add tomato paste, stir and cook for 1 minute.
Add diced tomatoes and oregano. Lower heat to a simmer and cook sauce for 10 minutes.
Add hot pepper flakes to taste.
Taste and adjust seasoning with salt and pepper.
Drain pasta reserving ¼ cup of the pasta water.
Add the pasta to the sauce and stir to combine. If the sauce seems dry, add some of the pasta water.
Plate the pasta and sauce in bowls and finish with a topping of freshly grated pecorino cheese.
Serve immediately.