In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the corn, peas, ketchup, Worcestershire sauce and garlic. Reduce heat; cover and cook for 5 minutes.

Combine the cornstarch, bouillon and water until well blended; stir into beef mixture. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in sour cream and heat through (do not boil).

Spread mashed potatoes over the top; sprinkle with cheese. Cover and cook until potatoes are heated through and cheese is melted.