Preheat your oven to 375°F (190°C).
Clean the Portobello mushrooms by wiping them with a damp cloth. Remove the stems and gills with a spoon to create space for the stuffing. Brush the mushrooms with olive oil on both sides and put them on a baking sheet. Use some parchment for easier clean up.
Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the chopped onion and ground turkey, breaking it up as it cooks. Allow the turkey to cook through and brown, about 5-7 minutes. Add the minced garlic and cook for another minute. Remove some of the extra fat but leave a little bit.
Stir in the spinach and sun-dried tomatoes, allowing the spinach to wilt, about 2-3 minutes. Add in salt, pepper and oregano, adjusting the seasoning as needed.
Remove from heat and stir in the feta cheese until combined.
In a medium sized bowl, add the breadcrumbs, the Parmesan cheese and remaining tablespoon of olive oil and mix together.
Divide the filling evenly among the Portobello mushrooms, pressing it down gently to pack it in.
Top with the breadcrumb mixture. For added crispiness, drizzle a little bit of olive oil over the top.
Bake the mushrooms for 20-25 minutes or until the mushrooms have softened and the top is crispy and brown.
Sprinkle the stuffed mushrooms with fresh parsley and serve hot.