Bring a pot of salted water to the boil.
Thinly slice onion. Heat olive oil in a frypan on medium. Cook onion for 4-5 minutes, until softened but not browned. Add pork nduja and measure of chilli flakes to the pan and cook for an additional 2 minutes, breaking up nduja with as it cooks, until slightly browned.
Add crushed tomatoes and salt measure to pan, bring to a simmer and cook for about 10 minutes, until slightly reduced. Season to taste with salt and pepper.
When sauce has 5 minutes remaining, cook pasta. Use hands to separate pasta well before cooking to prevent them from sticking together. Cook in pot of boiling water on high heat for 3 minutes, until tender. Drain well and return to pot.
Add pasta to pan with sauce and toss until well coated.
Spoon pasta into bowls and top with Parmesan.