1. Bring a large pot of salted water to a boil and cook the fettuccine until al dente according to package directions. Drain and set aside.

2. While the pasta cooks, heat a large skillet over medium heat. Add the olive oil and 1 tablespoon of butter.

3. Season the salmon fillets with 1 tablespoon of Cajun seasoning. Place the salmon in the skillet and cook for 3 to 4 minutes per side, until the salmon is flaky and fully cooked through. Remove the salmon from the pan and set aside.

4. In the same skillet, melt the remaining tablespoon of butter. Add the onion and sauté for about 2 minutes until softened. Stir in the garlic and cook for another minute.

5. Pour in the heavy cream and chicken broth. Bring the mixture to a gentle simmer, then stir in the remaining Cajun seasoning and parmesan cheese.

6. Let the sauce simmer for 3 to 5 minutes, stirring occasionally, until slightly thickened and creamy.

7. Add the spinach and cooked pasta to the skillet. Toss everything together and cook for about 1 minute, until the spinach wilts and the pasta is fully coated in the sauce.

8. Return the salmon to the skillet or serve it on top of the pasta. Garnish with extra parmesan cheese and serve warm.