Preheat oven to 400°.
Remove casing from sausage. Cook sausage in a large nonstick skillet over medium heat until browned, stirring to crumble. Add flour, and cook 2 minutes, stirring frequently. Add the mushrooms, milk, oregano, pepper, and clams; bring to a boil, stirring constantly. Reduce heat; simmer 5 minutes or until thick. Remove from heat. Stir in 1/2 cup cheese.
Place bread halves on a baking sheet; spread clam mixture evenly over cut sides of bread. Sprinkle with 1/4 cup cheese and parsley. Bake at 400° for 12 minutes or until golden brown. Cut each half into 3 pieces.