Cook the spaghetti in boiling, salted water. Drain, reserving about a third of a cup of the cooking water. Set aside.
In a large skillet over medium high heat, add 1 tbsp olive oil. Once hot, add the shrimp. Sprinkle with 2 tsp cajun seasoning and saute briefly until just cooked through - about 2-3 minutes. Remove to a plate and keep warm.
Add the remaining tbsp of oil to the pan as well as the shallot and red pepper. Saute until soft then add the diced tomatoes and cream. Stir in the remaining 1/2 tsp cajun seasoning.
Let sauce simmer for a couple minutes to thicken and then add your pasta and shrimp back in. Taste and season as needed. If sauce seems dry, add a splash of your cooking water.