In a large saucepan, cook beef over medium heat until no longer pink; drain. Stir in the ketchup, oregano, chili powder, salt and pepper. Bring to a boil. Reduce heat; cover and simmer for 10 minutes.
In a large bowl, combine the lettuce, tomatoes, cheese, olives and beef mixture. Combine mayonnaise and taco sauce; pour over salad and toss to coat. Sprinkle with corn chips. Serve immediately. Yield: 10 servings.