Carefully clean the portobello mushroom caps with a damp cloth and remove the stems.
In a large bowl, mix the halved cherry tomatoes, mozzarella balls, and chopped basil.
Drizzle the mixture with balsamic glaze, olive oil, garlic powder, and season with salt and pepper to taste. Stir gently to combine.
Place the portobello caps, gill-side up, on a baking sheet lined with parchment paper.
Spoon the Caprese mixture generously into each portobello cap, packing it slightly.
If desired, sprinkle grated Parmesan cheese on top of each stuffed mushroom.
Bake in the preheated oven for about 20 minutes, or until the mushrooms are tender and the cheese is melted and bubbly.
Remove from the oven and let cool for a couple of minutes before serving.
Notes
Serve on a rustic wooden board or white plate, garnished with extra fresh basil leaves and a drizzle of balsamic glaze around the edges for an elegant touch.