Add the shrimp to a medium mixing bowl and drizzle with 1-2 tablespoons of olive oil, Cajun seasoning, and dried oregano. Mix well to combine. Set aside to cook the sausage.
Heat a large cast iron skillet over high heat. Drizzle with approximately 1 tablespoon of olive oil swirling to coat the bottom of the skillet. Add the sausage in a single layer and cook each side for approximately 2-3 minutes. Remove the sausage to a clean plate and set aside.
Return skillet to medium-high heat. Add an additional drizzle of olive oil, if needed, and add the shrimp to the skillet in a single layer. Cook each side for approximately 1-2 minutes, or until just cooked or just nearly cooked. Remove from the skillet to a clean plate and set aside.
Bring a large pot of salted water to a rolling boil over high heat.
As the water boils, return the skillet to medium heat. Add a bit more olive oil and the onions to the skillet. Mix well and cook the onions for 3-4 minutes, stirring often. Add the diced bell pepper and continue to cook for an additional 2-3 minutes, stirring often. Add the garlic and cook for 30 seconds, stirring continuously.
Add the cajun seasoning and tomatoes to the pan. Mix well to combine.
Meanwhile, add the fettuccini noodles to the pot of boiling water. Use a large wooden spoon to stir the noodles and prevent them from sticking together. Cook until al dente.
Stir in the granulated sugar and chicken broth. Bring to a boil and reduce heat too low. Cover and simmer for approximately 5 minutes.
Stir in the heavy cream and butter and add the shrimp and sausage back to the pot. Increase heat to medium and bring to a simmer- do not boil the cream.
Stir in the cooked fettuccini noodles and shredded cheese, adding reserved pasta water as needed to thin the sauce.