Cook the mushrooms in a large skillet in the butter over moderately low heat, stirring until most of the liquid the mushrooms give off is evaporated. Add the flour and cook, stirring, for 3 minutes. Add the liquids in a stream, whisking and bring the mixture to a boil. Simmer for 3 minutes and stir in the 2 cheeses, the herbs, and salt and pepper, to taste.
Preheat the broiler.
Arrange the bread slices in one layer on a sheet pan. Divide the turkey slices evenly on top and spoon some of the sauce over each toast. Broil the slices for 2 to 3 minutes or until golden and top each toast with some of the bacon and some of the chives.