Preheat the oven to 400°F.
In a small bowl, combine melted butter, minced garlic, Italian seasoning, salt, and black pepper.
Brush the mixture generously over the portobello mushrooms, ensuring they are well coated.
Place the mushrooms, gill side up, on a baking sheet lined with parchment paper.
In a separate bowl, mix together the cherry tomatoes, mozzarella, and chopped basil.
Spoon the tomato and mozzarella mixture evenly into each mushroom cap.
Bake in the preheated oven for 15-20 minutes, until the mushrooms are tender and the cheese is melted.
Remove from the oven and drizzle with balsamic glaze before serving.