Melt 1/4 cup butter in a heavy saucepan. Stir in flour and cook
1 to 2 minutes, but do not brown. Add broth, sherry, cream, and
oregano. Cook, stirring constantly, until sauce comes to a boil. Add
1/4 cup Parmesan cheese, stirring until melted. Remove from heat.

Melt remaining butter with oil in skillet. Add garlic, scallions,
parsley, and mushrooms and saute until mushrooms are brown. Remove
from heat. Cook spaghetti according to package directions until al
dente. Drain well.

Combine sauce, mushrooms, spaghetti, and turkey; season with
salt to taste. Pour into greased casserole and sprinkle with
remaining cheese. Bake at 375 degrees for 15 minutes, or until bubbly.