In a large saucepan, cook the potato slices in lightly salted, boiling water for 12 to 15 minutes or until just tender. Drain.
In a heavy, large skillet, cook potatoes and onions in butter or margarine over medium-high heat until potatoes are lightly browned, turning often. Add parsley, garlic salt, pepper, thyme, sage, and rosemary; toss lightly. Spoon mixture into an ungreased 13x9x2-inch (3-quart rectangular) baking dish.
In the same skillet, cook sausage over medium-low heat until no pink remains, breaking meat into small pieces. Drain off fat. Spread the cooked sausage over potato mixture. Sprinkle evenly with shredded Swiss cheese or arrange cheese slices on top.
Bake in a 350 degree F oven for 20 to 25 minutes or until heated through. Makes 8 servings.