Preheat the oven to 220°C. Place the tomatoes and their juices, garlic, 4 T olive oil and chilli flakes into a large, deep, oiled baking tray. Top with the cauliflower.
Mix the cumin with the remaining olive oil and season to taste. Spoon over the cauliflower.
Bake for 20 minutes, then pour in ½ cup water or stock and stir the tomatoes around. Use to baste the cauliflower. Roast for a further 20 minutes, or until the cauliflower is bronzed and just tender.
Roughly mash the tomatoes and garlic in the pan, adding a little more water or stock if necessary. Check the seasoning. Serve the rough sauce with the cauliflower and coriander pesto, garnished with coriander.