In a large skilled, heat 1 tablespoon butter over medium-high heat. Add garlic and cook 1 minute.
Add parsley, shrimp, and vermouth. Cook 2 minutes, stirring constantly until shrimp is pink. Don't overcook! Transfer to a small bowl.
In same skillet, heat 3 tablespoons butter until melted. Reduce heat to low and add cream, parmesan, and red pepper flakes. Cook 3 minutes, stirring constantly, until cheese melts and sauce is smooth. Stir in salt and pepper.
Serve: Place fettuccine is a service dish; add shrimp then top with avocado. Toss gently.