In a medium bowl, combine lemon zest, lemon juice, vinegar (if using), turmeric, garlic, sugar and ½ teaspoon salt, and stir to dissolve the turmeric. Add the yogurt and mayonnaise and stir until smooth.

Mix in the dill and chicken. (Chicken salad can be made up to 3 days in advance. Store in an airtight container in the refrigerator.)