Preheat your broiler on high. Position an oven rack 6 inches below the heating element (not directly below).
Cut the tomatoes in half. Cut a tiny sliver from the bottom of each half, so that the tomatoes can stand upright without wobbling.
Spray the tomatoes all over with olive oil. Place them on a broiler-safe rimmed baking dish, cut side up.
Sprinkle the tomatoes with salt, pepper, garlic powder, and thyme. Top with Parmesan, 2 tablespoons for each tomato half.
Broil until the cheese is golden brown, 3-5 minutes.
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Notes
Make sure to keep a close eye on the tomatoes while they're in the oven. Even when not directly under the heating element, they can still burn quite easily. Broiling is always challenging in this way, and this recipe is no different.