Preheat Oven → 400°F / 200°C; line baking sheet with parchment.
Clean Mushrooms → Wipe caps, remove stems, scoop gills gently.
Pre-Bake Caps → Brush with olive oil, place upside-down, bake 5 minutes to release moisture.
Dice Filling → Small dice tomatoes and mozzarella so they fit neatly.
Mix Filling → Combine tomatoes, mozzarella, basil, garlic, salt, pepper.
Stuff Generously → Spoon filling into pre-baked caps; press lightly.
Drizzle Oil → Light brush or spray tops for golden edges.
Bake → 12–15 minutes until cheese is melted and bubbly.
Broil Finish → 1–2 minutes for golden tops (watch closely!).
Serve → Drizzle balsamic glaze, extra basil, and serve warm.