1Wash and remove stems from mushrooms, pat dry. Save stems for another recipe. In mixing bowl place clams, onion, garlic salt, minced garlic, butter and oregano. Mix through and blend well. Add Italian bread crumbs, egg, clam juice and blend. Stir cheeses in clam stuffing and mix well. Place clam mixture inside mushroom cavity and slightly mound clam mixture.
2Place mushrooms in slightly oiled baking dish. Pour butter over mushrooms. Cover and place in a preheated oven at 350 degrees F for about 35 - 40 minutes.
3Remove cover and sprinkle freshly grated mozzarella cheese on top and pop back in oven just so the cheese melts slightly, garnish with freshly diced parsley.