Cut each sausage into five pieces. Heat the oil in a frying pan or sauté pan that has a lid. Add the sausages and fry, stirring frequently, for 4 minutes or until lightly browned. Add the onion and garlic to the pan, and cook for 1 minute, then add the halved mushrooms. Stir-fry for 2 minutes, then stir in the tomatoes. Bring to the boil, cover and simmer gently for 5-10 minutes.
While the sauce is simmering, cook the pasta in a pan of salted boiling water for 12 minutes, or according to the pack instructions, until tender with a bite at the centre.
Add the peppers to the sauce with the crushed chilli flakes and plenty of black pepper, and heat through for 1 minute.
Drain the pasta and turn into a warmed serving bowl. Taste the sauce and adjust the seasoning, then pour over the pasta and toss gently to combine. Serve immediately.