Bring a large pot of lightly salted water to a rolling boil.

Boil fettuccine until cooked through yet firm to the bite, about 8 minutes; drain and transfer pasta to a large serving bowl.

Heat butter and garlic in a large skillet over medium-high heat; stir in sausage, tomatoes, broccoli, bell pepper, mushrooms, and green onion.

Cook and stir until sausage is browned and vegetables are tender.

Stir in chicken, shrimp, white wine, Cajun seasoning, milk, and 1/4 cup Parmesan cheese. Cook and stir shrimp until they are bright pink on the outside and meat is no longer transparent in the center, 3 to 5 minutes.