Remove stems, clean portobellos and wipe dry. Lay open side up and lightly season inside with a pinch of salt and pepper
Place on tray and bake for 15 minutes, then remove. If it has filled with liquid, use tongs to flip over and empty.
Sprinkle with a pinch of oregano, place a few tomato halves inside and spoon crumbled feta over. Place under broiler for 5-8 minutes, until feta is melted and lightly browned.
Transfer to serving plate, garnish with basil. Lightly drizzle with olive oil and balsamic and enjoy!