In a medium bowl, combine the shrimp, olive oil, and Cajun seasoning. Let marinate for at least 15 minutes.

In a large pot, bring salted water to a boil. Add fettuccini pasta and cook until al dente, about 8–10 minutes. Drain and set aside.

In a large frying pan, melt butter over medium heat. Add mushrooms and shallots, sauté for 5–6 minutes until golden.

In the same pan, add shrimp in a single layer. Cook for 2–3 minutes on each side until pink and charred. Remove and keep warm.

Pour chicken broth into the pan and bring to a boil, reducing to ¼ cup in 2–3 minutes.

In a bowl, blend sour cream and cornstarch until smooth. Whisk in remaining chicken broth. Add to reduced broth, stirring until thick and bubbly.

Return the mushrooms, shrimp, roasted bell peppers, and capers to the sauce, stirring gently to combine and heat through.

Ladle the shrimp and sauce over cooked fettuccini and serve immediately.