Sprinkle shrimp generously with cayenne pepper and cook on the grill until pink. While shrimp is cooking cook fettuccine until al dente, drain and set aside.
In large frying pan or dutch oven caramelize chopped onion in butter (season with salt and pepper). Add minced garlic and cook for another minute or two be careful not to burn garlic. Add chicken broth to onion mixture and simmer for about 5 minutes. Now add crushed tomatoes, paste, salt, pepper, and Cajun seasoning. Let simmer another few minutes. Add heavy cream and simmer five minutes. Now add pasta and parmesan cheese to sauce and let simmer for another 5 minutes. Remove from heat. Toss in shrimp. Serve adding fresh basil sprinkled over the top of pasta.