Heat oven to 350°F. In large nonstick skillet, cook ground beef and onion over medium-high heat for 5 to 7 minutes or until beef is thoroughly cooked, stirring frequently. Drain.
Add mixed vegetables and sandwich sauce; mix well. Bring to a boil. Reduce heat; simmer 5 minutes or until vegetables are tender, stirring occasionally. Spoon into ungreased 8-inch square (2-quart) glass baking dish.
Meanwhile, cook mashed potatoes as directed on package, using hot water, milk and margarine. Let stand 5 minutes. Spoon or pipe potatoes around edges of hot beef mixture. Sprinkle paprika over potatoes.
Bake at 350°F. for 25 to 30 minutes or until bubbly and thoroughly heated.