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

Bring a large pot of salted water to a boil. Add fettuccini and cook for 8–10 minutes. Drain and set aside, reserving a cup of pasta water.

In a frying pan, melt butter over medium heat. Add mushrooms and shallots, cooking for 4–5 minutes until tender. Remove from pan.

In the same pan, increase heat slightly and add marinated shrimp. Cook for 2–3 minutes per side until pink and opaque. Remove shrimp.

Pour in chicken broth, scraping up bits from the bottom. Bring to a boil and reduce to about ¼ cup, around 3-4 minutes.

Whisk together sour cream and cornstarch until smooth. Slowly add reduced broth, stirring continuously. Pour back into the pan and simmer for 3-4 minutes until thick.

Return shrimp, sautéed vegetables, roasted red bell peppers, and capers to the pan. Toss everything together, season with salt and pepper, and serve over fettuccini.