Prepare: Preheat the oven to 375°F (190°C). Clean the mushrooms and remove the stems.
Cook Tomatoes: In a pan, heat the olive oil and saute the tomatoes and garlic until soft.
Fill Mushrooms: Spoon the tomato mixture into the mushroom caps. Top each with crumbled feta cheese and sprinkle with oregano.
Bake: Place the stuffed mushrooms on a baking tray and bake for 20 minutes or until the mushrooms are tender and the cheese is melted.
Serve: Serve the Mediterranean Stuffed Portobello Mushrooms with Tomatoes hot from the oven.