1. Spray large skillet with cooking spray. Heat over medium-high heat. Place tortilla pieces in skillet. Cook 4 minutes or until lightly browned. Remove from skillet.
2. Cook ground beef in skillet until no longer pink; drain. Stir in drained tomatoes, corn and beans. Bring to a boil. Simmer 2 minutes or until hot. Add tortilla pieces and stir to coat.
3. Sprinkle with cheese and green onions. Cover. Let stand 5 minutes or until cheese is melted. Serve with sour cream, if desired.