1) Preheat oven to 190C/Gas 5. Spray a large, shallow baking dish with cooking spray.
2) Cut the peppers in half lengthwise, removing the seeds but leaving the stem. Although the stem is not edible it looks good in this dish and helps the pepper retain its shape. Place the peppers cut side up in the baking dish.
3) Divide the sliced garlic and the olives evenly among the peppers. Cut each tomato into 8 wedges and put 4 wedges into each pepper. Drizzle each stuffed pepper with a little oil and season with a few grinds of pepper.
4) Roast the peppers for about 50 minutes or until they are tender and beginning to brown around the edges.