For the filling: Cook the red onions in the oil over low heat until softened, about 5 minutes. Stir in the pomegranate juice, tomato paste, harissa and za'atar. Remove from the heat and set aside.
For the crust: Stir together the flour, cumin, garlic powder and salt in a large bowl. Then, using a pastry cutter or two knives, cut in the butter until you have a coarse meal with some pea-size butter lumps. Drizzle in the oil and a few drops of ice water and continue stirring together with a fork until a dough just comes together. Gather into a ball, flatten into a disk, and then wrap and refrigerate for 1 hour.
Preheat the oven to 400 degrees F.
Roll the dough out thinly on a lightly floured surface. With a 4-inch cutter, cut out 8 rounds.
On 4 of the rounds, layer on some of the onion mixture, some eggplant and zucchini slices, and a sprinkling of parsley, leaving an empty border. Cover with the remaining 4 pastry rounds and pinch the edges shut. Transfer the tartlets to a baking sheet.
Bake until lightly golden all over, about 20 minutes.
For the labneh: Meanwhile, stir together the yogurt, sour cream, goat cheese, mint, parsley, garlic, lemon zest, a drizzle of olive oil, and salt, pepper and za'atar to taste.
Serve the tartlets with a dollop of labneh on the side.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.