Add a good splash of oil to a heavy-based casserole dish and fry the onion for 5 minutes until soft but not coloured. Add the peppers, mushrooms and garlic and cook for a further 2 minutes. Slice the sausages to remove the skin and tear the meat in to chunks and put into the pan, then cook over a medium heat for 4-5 minutes. Add the paprika, the salt and pepper and stir.