Preheat the oven to 180°C/gas mark 4. Arrange the tomato slices cut-side up on a wire rack then drizzle over a little of the olive oil and season. Roast for 1 hour 30 minutes.
Meanwhile, cut the ciabatta into 8 thick slices, arrange on a baking sheet and brush all over with the remaining oil. Put in the oven and bake for 3-4 minutes, turning halfway though cooking, until crisp and golden.
Serve the bruschetta topped with the roasted tomatoes and the thyme scattered over the top.