Preheat your oven to 400°F and line a baking sheet with parchment paper.
Clean the portobello mushrooms with a damp cloth, remove the stems, and gently scrape out the dark gills with a spoon.
In a large skillet over medium heat, add the olive oil and ground turkey, breaking it apart until fully browned.
Add the minced garlic, sea salt, black pepper, and dried oregano to the skillet, cooking for another minute until fragrant.
Stir in the fresh spinach and cook just until wilted, then remove the skillet from the heat.
Place the mushroom caps on the prepared baking sheet and fill each one generously with the turkey and spinach mixture.
Sprinkle the crumbled feta cheese over the top of each stuffed mushroom.
Bake for 15 to 20 minutes until the mushrooms are tender and the cheese is lightly golden.
Garnish with fresh chopped parsley before serving.