Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
Clean the portobello mushrooms with a damp paper towel, remove the stems, and use a spoon to gently scrape out the dark gills.
Heat the olive oil in a non-stick skillet over medium-high heat.
Add the ground turkey to the skillet, breaking it up with a spatula, and cook until browned and fully cooked through.
Stir in the chopped spinach, dried oregano, garlic powder, sea salt, and black pepper, cooking for 1-2 minutes until the spinach is wilted.
Place the mushroom caps on the prepared baking sheet, hole-side up, and divide the turkey and spinach mixture evenly between them.
Sprinkle the crumbled feta cheese over the top of the stuffed mushrooms.
Bake in the oven for 15 to 20 minutes until the mushrooms are tender and the cheese is slightly golden.
Remove from the oven and drizzle each mushroom with the balsamic glaze.
Garnish with freshly chopped parsley and serve immediately.