In a medium bowl, combine peeled shrimp with olive oil and Cajun seasoning, ensuring each piece is well-coated. Let the shrimp marinate for about 10 minutes.

In a large pot, bring lightly salted water to a rolling boil. Add the fettuccini and cook for 8-10 minutes until al dente. Drain and set aside.

In a large frying pan, melt butter over medium heat. Add sliced mushrooms and shallots, sautéing for 5-7 minutes until tender.

Add the marinated shrimp to the same pan over medium-high heat. Cook until pink and opaque, about 2-3 minutes per side.

Pour chicken broth into the pan, bring to a boil, and simmer until reduced by half, about 2-3 minutes.

In a small bowl, mix sour cream and cornstarch until smooth. Stir into the reduced broth and cook until thickened.

Return sautéed shrimp and vegetables to the pan. Stir in roasted bell peppers and capers, heating through while seasoning to preference.

Plate the cooked fettuccini, then ladle the creamy mixture over the top. Garnish as desired.