Cook ground beef in a large skillet, stirring until it crumbles and is no longer pink; drain well, and set aside. Wipe skillet clean.
Sauté onion in hot oil in skillet over medium-high heat until tender. Add flour, stirring well; stir in water. Cook, stirring constantly, over medium-low heat, until thickened. Add bouillon and next 3 ingredients, stirring well. Add beef and thawed vegetables; stir well.
Spoon beef mixture into a lightly greased 2-quart casserole dish. Spread Walnut Mashed Potatoes over beef mixture; sprinkle with Parmesan cheese. Lightly sprinkle with paprika.
Bake, uncovered, at 350° for 30 minutes or until hot and bubbly.