Step 1Heat the oven to 425 degrees.
Step 2In a mixing bowl combine the tomatoes with the olive oil, cumin, sugar, garlic, thyme, oregano sprigs, lemon strips, ½ teaspoon salt and a good grind of pepper. Mix to combine, then transfer to a baking sheet just large enough — about 6 inches by 8 inches — to fit all the tomatoes together snugly. Place the sheet about 2 inches beneath the broiler and roast until the tomatoes are beginning to blister and the liquid is bubbling, about 20 minutes. Turn the oven to the broil setting and broil until the tomatoes start to blacken on top, 6 to 8 minutes.
Step 3While the tomatoes are roasting, combine the yogurt with the grated lemon zest and ¼ tsp of flaked salt. Keep in the fridge until ready to serve.
Step 4Once the tomatoes are ready, spread the chilled yogurt on a platter with a lip or in a wide, shallow bowl, creating a dip in it with the back of a spoon. Spoon the hot tomatoes on top, along with their juices, lemon strips, garlic, and herbs, and finish with the oregano leaves and chile flakes. Serve at once.