In a medium skillet, cook and stir ground beef and onion over medium-high heat until meat is brown and onion is tender. Drain thoroughly. In a bowl, combine meat mixture, taco sauce, half of the sour cream and salt. Cover and chill for 20 to 30 minutes. To serve, place lettuce on 4 individual plates. Sprinkle with cheese and tomatoes. Spoon meat mixture over salads. Top with remaining sour cream and garnish with olive slices. Serve with tortilla chips.