Place a large pot over medium heat and add in the olive oil. Add in the guanciale (or pancetta) and cook until brown and crispy, about 5-7 minutes. Reserve 1 tablespoon of the meat – set aside in a small bowl.
Add in the onions and red pepper flakes and cook for 3-5 minutes or until onions are translucent. Add in the tomatoes and raise the heat to medium-high and bring to a boil. Season with salt, reduce to a simmer at low heat and let cook for 30 minutes.
Meanwhile, peel and spiralize the parsnips, using Blade C. After the sauce has cooked for 30 minutes, add in the parsnip noodles, toss to combine thoroughly and let cook for 10 minutes or until parsnips are al dente.
Divide the pasta mixture into bowls and garnish with cheese and the reserved meat.