Preheat the oven to 210°C. Combine the oil, garlic and rosemary in a 33 x 23 cm glass baking dish. Place in the oven and, when the oil is hot but not smoking, add the cauliflower. Roast, turning the cauliflower occasionally, for 20 minutes or until lightly browned.
Add the tomatoes and salt to taste, tossing well. Roast for 20 minutes or until the tomatoes are hot and the cauliflower is tender.