In a large skillet, cook the beef and onion over medium heat until the meat is no longer pink: drain.
Stir in the corn, peas, ketchup, Worcestershire sauce and garlic. Reduce heat; cover and simmer for 5 minutes.
Meanwhile, dissolve bouillon in boiling water. Combine corn starch and sour cream until smooth: stir into beef mixture. Add bouillon. Spread mashed potatoes over the top; sprinkle with cheese. Cover and cook until potatoes are heated and cheese is melted.