Heat the oven to 425 degrees, with the rack arranged in the center of the oven.
Put the eggplant, tomatoes, red onion and garlic in a roasting pan large enough to hold the vegetables snugly in one layer. Add the olive oil, cumin, coriander, cayenne and salt. Toss to coat the vegetables evenly.
Roast the vegetables for 20-25 minutes, stirring halfway through. The eggplant should be golden brown and the tomatoes juicy and wrinkled.
While the vegetables are in the oven, cook the farro in boiling salted water until the grains are puffed and tender, about 20 minutes. Drain.
Dump the farro into the roasting pan with the roasted vegetables. Let everything cool 10 minutes.
Add the vinegar, parsley and feta cheese. Transfer the salad to a serving bowl and serve warm, or at room temperature.
Enjoy the salad warm or at room temperature or keep refrigerated up to 3 days.