In a medium bowl, combine the peeled and deveined shrimp with olive oil and Cajun seasoning. Let marinate for at least 10 minutes.

Bring a large pot of salted water to a rolling boil. Add fettuccini pasta and cook for 8-10 minutes until al dente. Drain and set aside.

In a large skillet, heat butter over medium heat. Add chopped mushrooms and shallots, and sauté for 5-7 minutes until tender.

In the same skillet, add the marinated shrimp. Cook for 2-3 minutes until pink and opaque, then remove from skillet.

Pour chicken broth into the skillet and bring to a boil. Boil gently for 2-3 minutes until reduced by half.

In a small bowl, mix sour cream and cornstarch until smooth. Gradually stir into the broth, cooking over medium heat until thickened.

Return shrimp, sautéed vegetables, roasted red bell peppers, and capers to the skillet. Stir gently to combine and heat through for 2 minutes.

Serve by plating cooked fettuccini first and spooning the creamy shrimp mixture over the top. Garnish with fresh herbs if desired.