Combine the fat-free plain yogurt, mustard and chives in a bowl and mix well. Spread the Gruyere cheese evenly over one side of each tortilla. Top each one with 1/4 cup of the Swiss cheese. Layer the lettuce and turkey ham over the cheese, leaving a 1/2-inch border around the edges. Roll each one up tightly and wrap in plastic wrap. Refrigerate for at least 45 minutes before serving.
To serve, cut each roll diagonally in half.