Heat the oven to 200oC (400oF)
Put the tomatoes in a rimmed baking dish that’s just large enough to accommodate them all snugly. Add the oil, cumin, sugar, garlic, thyme, oregano sprigs, lemon strips, a pinch of salt and a good grind of pepper. Toss together with your hands.
Roast for 20 minutes, until the tomatoes are beginning to blister and the liquid is bubbling, then turn the oven to the grill setting and grill for 5 to 7 minutes, until the tomatoes start to blacken on top.
While the tomatoes are roasting, mix the yoghurt with the grated lemon zest and 1/4 tsp salt, then return to the fridge.
Once the tomatoes are ready, spread out the cold yoghurt on a large plate or shallow, wide bowl. Spoon the hot tomatoes on top, as well as the pan juices, lemon peel, garlic and herbs, and finish with the remaining oregano and chilli. Serve at once with some flatbreads or sourdough.