Preheat oven to 375° F. Line a large baking sheet with parchment paper or spray with cooking spray.
Lay tomatoes onto the baking sheet, cut side up. Top each tomato with Parmesan cheese, oregano and salt and pepper. Drizzle the tablespoon of olive oil evenly over all the tomatoes.
Bake for 12 – 15 minutes, or until tomatoes are tender and cheese is melted. Serve immediately.