In a mixing bowl, combine the halved cherry tomatoes, mozzarella balls, chopped basil, garlic, balsamic vinegar, olive oil, and a pinch of salt and pepper. Mix well to combine.
Place the portobello mushrooms on a baking sheet, gill side up. Drizzle a bit of olive oil over each mushroom and sprinkle with salt and pepper.
Spoon the tomato and mozzarella mixture evenly into each portobello mushroom, filling them generously.
Sprinkle the grated Parmesan cheese over the stuffed mushrooms.
Bake in the preheated oven for about 20-25 minutes, or until the mushrooms are tender and the cheese is melted and bubbly.
Once out of the oven, drizzle with balsamic glaze for added flavor and garnish with extra fresh basil leaves if desired.
Notes
Serve on a rustic wooden board or individual plates, garnished with additional basil leaves and balsamic glaze.