Preheat your oven to 375°F (190°C).
Prepare the portobellos by gently removing the stems to create cups. Place them on a baking sheet lined with parchment paper or in any ceramic baking dish you like. Here is a good option from Amazon.
Add a layer of mozzarella cheese to each mushroom cap.
Top with feta cubes and halved cherry tomatoes.
Sprinkle more mozzarella on top to create a nice cheesy cover.
Season with salt, pepper, and a sprinkle of basil and oregano.
Bake for about 20 minutes, or until the cheese is melted, bubbly, and slightly browned.
Drizzle balsamic vinegar over the mushrooms right before serving (optional but highly recommended!).
Serve warm and enjoy!