Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Gently wipe the portobello mushrooms with a damp paper towel to remove dirt, then remove the stems and use a spoon to scrape out the dark gills.
Finely chop the mushroom stems and set them aside.
In a large skillet over medium heat, add the extra virgin olive oil and the minced garlic, sautéing until fragrant.
Add the ground turkey and chopped mushroom stems to the skillet, breaking the meat apart with a spatula until it is fully browned and cooked through.
Stir in the fresh spinach, sea salt, black pepper, and dried oregano, cooking just until the spinach has wilted.
Place the mushroom caps on the prepared baking sheet, gill-side up, and divide the turkey and spinach mixture evenly between the two caps.
Sprinkle the crumbled feta cheese over the top of each stuffed mushroom.
Bake for 15 to 18 minutes until the mushroom caps are tender and the cheese is lightly golden.
Garnish with fresh chopped parsley before serving.