1Heat oven to 350°F. In 12-inch skillet, cook beef and onion over medium-high heat 5 to 7 minutes, stirring occasionally, until beef is thoroughly cooked; drain.
2Stir in taco seasoning mix, soup, beans and corn; heat to boiling. Reduce heat to low; simmer uncovered 8 to 10 minutes, stirring occasionally, until sauce is slightly thickened.
3Meanwhile, place tortilla chips in 13x9-inch (3-quart) glass baking dish. Sprinkle cheese over chips. Bake 4 to 5 minutes or until cheese is melted.
4Spread cooked beef mixture evenly over melted cheese. Top with tomato, lettuce and sour cream. Serve immediately.