Heat the oven to 200 C / 400 F.
In a 23 cm / 9-inch baking dish, toss the cherry tomatoes, olives, garlic, olive oil, dried oregano, red pepper flakes, and a pinch of black pepper.
Roast for 10 minutes, until the tomatoes start to soften and blister.
Remove the dish and nestle the halloumi slices between the tomatoes, pressing them slightly into the juices.
Return to the oven and roast for 12 to 15 minutes, until the halloumi is soft, the edges are light golden, and the tomatoes have collapsed into a light sauce.
For extra color, switch the oven to broil for 2 minutes, watching closely so the cheese doesn't turn tough.
Remove from the oven and squeeze the lemon half over the top. Scatter fresh oregano or parsley over everything.
Serve warm, straight from the dish, with warm bread for scooping up the juices.