Add a drizzle of oil to a large pan over medium-high heat. Add the sausages and fry until deep golden all over, turning frequently, then remove and place them to one side. Slice them into 5-6 pieces just before needed. Don't worry about cooking the sausages right through; this is just about browning the outside and rendering down the fat.
Add the peppers and onion to the leftover fat and fry until soft and golden. Lower the heat slightly, then make space in the centre for the garlic and fry for a minute or so. Stir in tomato paste and fry for another minute or so.
Pour in the tomatoes, then fill one of the cans about half the way up with water. Use this to swill out both of the cans and pour that in too. Add in the oregano, basil, chilli flakes and a good pinch of salt and pepper. Give it a stir and burst some of the tomatoes with your wooden spoon. Stir in the slices of sausage, then bring to a gentle simmer. Cook for 30 minutes, or until the sauce has thickened and is no longer watery, stirring occasionally and gently bursting the chunks of tomato as needed. This time is important to reduce the sauce and marry all the flavours together.
Just before the sauce is done, add the pasta to salted boiling water and cook until al dente. Retain 1/2 cup or so of the leftover pasta water as you drain it.
Stir the pasta into the sauce, then stir in the parmesan and parsley. If you need to thin out the sauce slightly, just add a splash of starchy pasta water (discard otherwise). The sauce should be lusciously thick, cling to the pasta and no longer be watery at all. Continue tossing until it reaches this consistency.
Check for seasoning and adjust (generously if needed) with more salt and pepper to taste. Serve up with extra parmesan and parsley if desired and enjoy!