Preheat your oven to 400°F and line a baking sheet with parchment paper for easy cleanup.
Gently wipe the portobello mushroom caps with a damp paper towel to remove any debris and carefully scoop out the gills using a spoon.
Brush the outside of each mushroom cap with the olive oil and place them gill-side up on the baking sheet, roasting for 10 minutes until slightly softened.
While the mushrooms roast, heat a non-stick skillet over medium-high heat and add the ground turkey, breaking it apart with a wooden spoon.
Season the turkey with garlic powder, dried oregano, sea salt, and black pepper, cooking until the meat is no longer pink.
Toss in the fresh spinach and stir for 1-2 minutes until it is completely wilted and incorporated into the meat mixture.
Remove the skillet from the heat and allow it to cool for a minute before folding in the Greek yogurt to create a luscious, creamy texture.
Divide the turkey and spinach mixture evenly between the pre-roasted mushroom caps and sprinkle the tops with parmesan cheese.
Return the stuffed mushrooms to the oven and bake for an additional 8-10 minutes until the cheese is melted and the filling is heated through.