In a large bowl, combine the yogurt, olive oil, grated garlic, finely chopped cilantro, and a pinch of salt. Mix thoroughly, then refrigerate covered to allow the flavors to come together until the carrots are done.
Preheat the oven to 375°F.
Thoroughly clean the carrots, and cut off the leafy stems. Dry throughly.
Arrange the carrots in a single layer on a large sheet tray. Drizzle them generously with olive oil and a heavy pinch of salt.
Add the za'atar and sumac and throughly coat.
Roast for 30-40 minutes or until fork tender.
When ready to serve speed the yogurt sauce on the bottom of a large dish then top with the warm carrots.
