Cut the red peppers in half lengthways, then scoop out and discard the cores and seeds. Put the pepper halves, cut-sides up, in a roasting tin lined with foil or a ceramic dish. Divide the garlic and thyme between them and season with salt and pepper.
Put a tomato half in each pepper and drizzle with the oil and vinegar. Roast in a preheated oven, 220°C (425°F), Gas Mark 7, for 55 minutes–1 hour until the peppers are soft and charred.
Serve with some crusty bread to mop up the juices and a baby leaf salad, if you like.