Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Gently remove the stems from the portobello mushrooms and use a spoon to scrape out the dark gills; discard both.
Place the mushroom caps on the prepared baking sheet, gill-side up, and lightly brush the edges with a tiny bit of the olive oil.
In a medium skillet over medium-high heat, add the remaining olive oil and sauté the diced onion until translucent, about 3-4 minutes.
Add the ground turkey to the skillet, breaking it apart with a wooden spoon, and cook until browned and no longer pink.
Stir in the minced garlic, dried oregano, dried basil, sea salt, and black pepper, cooking for another 1-2 minutes until fragrant.
Spoon the turkey mixture evenly into the mushroom caps, pressing down slightly to pack the filling firmly.
Bake in the preheated oven for 15-18 minutes until the mushrooms are tender and the filling is golden.
Remove from the oven, sprinkle with grated parmesan cheese and fresh parsley, then finish with a drizzle of balsamic glaze before serving.