Pat the shrimp dry on a piece of kitchen paper and toss with the Cajun seasoning. Set aside.
Cook the pasta in a pan of boiling salted water as per the packet instructions. Start checking for doneness around the 12 minute mark. Once it is cooked, drain and set aside reserving a little of the pasta cooking water.
Meanwhile, heat a large non-stick frying pan over a medium high heat. Add 1/2 tbsp of the oil and cook the shrimp until just pink on each side. Remove from the pan and return to the bowl with any leftover Cajun seasoning with a slotted spoon.
Add the sliced onion, chopped bell pepper and a generous pinch of salt to the pan along with the remaining 1 tbsp of oil. Reduce the heat to medium and fry for about 8-10 minutes until the onions are just starting to take on some color and the bell pepper is starting to soften. Stir in the minced garlic and cook for a further minute, until aromatic.
Pour in the wine or chicken broth and using your wooden spoon scrape up any browned bits from the bottom into the sauce. Allow to bubble away for about 2 minutes to cook off the alcohol and slightly reduce the sauce before stirring in the tomatoes. Cook for a few more minutes until the tomatoes are starting to break down into the sauce.
Stir in the heavy cream, then the cooked pasta and the cooked shrimp, including any residual Cajun seasoning from the bowl. Stir until combined, adding a little pasta cooking water if the sauce is not clinging to the pasta or is too thick.
Once the pasta and shrimp are heated through and the sauce has reached the desired consistency remove from the heat and stir in the shredded parmesan. Add lemon juice and black pepper to taste, and salt if it is needed. Serve with a little extra parmesan and some parsley scattered over each bowl.