In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the soup, peas and carrots, mushrooms, water, rosemary, 1/2 teaspoon garlic powder, salt and pepper; heat through. Transfer to a greased 9-in. deep-dish pie plate.
In a large bowl, beat the mashed potatoes, cream cheese, sour cream and remaining garlic powder until blended. Spread over top. Sprinkle with Parmesan cheese.
Bake, uncovered, at 350° for 20-25 minutes or until heated through and potatoes are lightly browned. Yield: 6 servings.