Cook Pasta
Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente. Drain and set aside.
Cook Sausage
In a large skillet over medium-high heat, add olive oil and sausage. Sear until browned, about 3–4 minutes per side. Remove from pan and set aside.
Sauté Shrimp
Season shrimp with Cajun seasoning. In the same pan, add a touch of oil if needed and cook shrimp for 1–2 minutes per side until just pink. Remove and set aside.
Sauté Veggies
Lower heat to medium. Melt butter in the skillet, then add onions and bell pepper. Sauté 4–5 minutes until softened. Stir in garlic and cook another 30 seconds.
Make Sauce
Whisk in tomato paste, then pour in chicken broth and heavy cream. Simmer 3–4 minutes until slightly thickened. Stir in Parmesan cheese and 1 tablespoon Cajun seasoning. Adjust salt to taste.
Combine
Return sausage and shrimp to the skillet along with the cooked pasta. Toss everything together until well coated and heated through.
Serve
Garnish with chopped parsley and red pepper flakes if desired. Serve immediately.