Mix all ingredients for the Cajun spice mix. If using previously frozen and defrosted shrimp, pat it dry with paper towel to get rid of excessive moisture. Add the shrimp to the bowl with the seasoning and toss until all shrimp is evenly coated.
Bring a pot of water to a boil, add salt, then the pasta and cook according to package instructions. Reserve ½ cup of pasta water before draining.
While the pasta is cooking, heat 1 tbsp of olive oil in a pan, then add shrimp and cook for 1- 2 minutes on each side. Depending on the size of the shrimp. Remove from the pan.
To the same pan add sliced green pepper and cook on medium-high heat for 5 minutes. You should see nice colour on your pepper slices. Remove to the same plate with shrimp.
Lower the heat and add 2 cloves of minced garlic and cook for 30 seconds, then add crushed tomatoes, a pinch of salt, heavy cream and Parmesan cheese. Add a splash of reserved pasta water if needed. Add the drained pasta, shrimp and green peppers to the sauce, and toss to combine, season with salt to taste. Serve topped with sliced green onions and more Parmesan cheese.