In a mixing bowl, combine shrimp with olive oil and Cajun seasoning. Marinate for 10-15 minutes.

Bring a pot of salted water to a boil. Cook fettuccini according to package directions until al dente, about 8-10 minutes.

In a frying pan, melt butter over medium heat. Sauté mushrooms and shallots until tender, about 4-5 minutes, then remove.

In the same pan, cook marinated shrimp over medium-high heat for 2-3 minutes until pink and opaque. Remove from pan.

Pour chicken broth into the pan and reduce to ¼ cup for 2-3 minutes. Scrape browned bits for flavor.

Mix sour cream and cornstarch until smooth; gradually add to reduced broth, stirring until it thickens.

Combine cooked shrimp and vegetables with the sauce, heating for 1-2 minutes until warmed through.

Plate fettuccini and spoon over the shrimp mixture. Garnish with fresh herbs if desired, and serve promptly.