Ground dried lemon (lemon omani) is used in Persian cooking to flavor classic dishes such as Khoresht Gheymeh Bademjan, a beef and eggplant stew. The ground lemon lends an "earthy citrus" flavor to the stew. To produce the dried lemons (or limes) the fruit is typically boiled in a brine solution then dried. They may be sold whole, crushed or ground.
You can purchase dried ground lemon or dried ground lime from Middle Eastern grocery stores You can also find it online at Amazon.com: Sadaf Lemon Omani.