Grease 9 x 13 baking dish. Cover bottom with half the bread cubes. Fry onions in butter until translucent. Set aside. Layer mettwurst over bread cubes. Combine cheeses and sprinkle over mettwurst. Layer with remaining bread cubes. In large bowl, whisk together fried onions, eggs, milk, salt and Italian seasoning. Pour evenly over bread cubes. Sprinkle with parsley. Refrigerate several hours or overnight. When ready to bake, heat oven to 350°. Bake uncovered for 50 minutes. Let stand 10 minutes before serving.