In 10-inch nonstick skillet, cook beef and onion over medium-high heat, stirring frequently, until beef is thoroughly cooked; drain.
Add all remaining Stew ingredients; mix well. Heat to boiling. Reduce heat to low; simmer 8 to 10 minutes, stirring occasionally, until vegetables are tender.
Meanwhile, in medium saucepan, heat water, margarine and garlic salt to boiling. Remove from heat; add milk. Stir in potato flakes and parsley. Cover to keep warm.
To serve, fluff potatoes with fork. Serve stew over potatoes.