Bring a large pot of lightly salted water to a boil. Cook pasta for 8 to 10 minutes, or until al dente; drain.
Melt butter with olive oil in a large skillet over medium heat. Saute garlic and mushrooms until tender. Stir in crawfish and green onions; reduce heat to low, and cook 5 minutes. Stir in half and half, Parmesan cheese, and parsley. Simmer for 5 minutes. Season with salt and pepper, and serve over hot linguine.