Remove the sausage meat from the casings using scissors.
Heat the 1 tbsp olive oil in the pan. Add the sausage meat and break apart with the back of a wooden spoon. Cook until the sausage meat begins to brown. Remove from the pan and set aside.
Heat the remaining oil. Add the fennel and peppers and cook for 3-4 minutes. Then add the garlic, fennel seeds, oregano, rosemary, and nduja. Cook for 1 minute.
Add the passata and bring to a gentle boil, then reduce to a simmer. Season to taste. Cook for 15-20 minutes until the sauce has thickened.
In the meantime, bring a pan of salted water to the boil. Add the rigatoni and cook for 10–12 minutes until al dente.
Drain the pasta, then mix it with the sausage sauce. Spoon into serving bowls and top with as much grated parmesan as you like