Preheat your oven to 400°F and line a baking sheet with parchment paper for easy cleanup.
Gently wipe the portobello mushrooms with a damp paper towel to remove any dirt, then pop out the stems and use a spoon to carefully scrape out the dark gills.
Heat the olive oil in a large skillet over medium-high heat, add the ground turkey, and cook until browned, breaking it up into small crumbles.
Stir in the minced garlic, dried oregano, sea salt, and black pepper, cooking for 1 minute until the aromatics are fragrant.
Add the chopped spinach and fresh parsley to the skillet, tossing until the spinach is just wilted and the mixture is well combined.
Place the mushroom caps on the prepared baking sheet, gill-side up, and divide the turkey and herb mixture evenly among them.
Roast in the oven for 15 to 18 minutes until the mushrooms are tender and the stuffing is golden.
Remove from the oven and finish with a drizzle of balsamic glaze for a sweet and tangy pop of flavor.