Heat oven to 325°F. In large skillet, brown ground beef, onion and bell pepper over medium-high heat until beef is thoroughly cooked, stirring frequently. Drain.
Add sandwich sauce and corn; mix well. Reduce heat; simmer 4 to 6 minutes or until thoroughly heated and corn is crisp-tender, stirring occasionally.
Meanwhile, in medium saucepan, bring water and garlic salt to a boil. Remove saucepan from heat; stir in potato flakes until well blended. Add sour cream and egg; mix well.
Spoon beef mixture into ungreased shallow 2-quart casserole. Spoon potato mixture in circle around edges of casserole. Sprinkle potatoes with cheese.
Bake at 325°F. for 25 to 30 minutes or until potatoes are set. If desired, sprinkle potatoes with chopped fresh parsley.