Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Clean the portobello mushrooms with a damp cloth, remove the stems, and gently scrape out the gills with a spoon.
Mince the garlic and finely chop the fresh parsley and thyme.
In a medium skillet over medium heat, add the olive oil and sauté the ground turkey and garlic until the turkey is browned and cooked through.
Add the fresh spinach to the skillet and stir until just wilted, then remove from heat and let cool slightly.
In a mixing bowl, whisk the egg and then stir in the Greek yogurt, sea salt, black pepper, parsley, and thyme.
Fold the turkey and spinach mixture into the yogurt mixture until well combined.
Place the mushroom caps on the prepared baking sheet, stem-side up, and divide the filling evenly between the two caps.
Sprinkle the parmesan cheese over the top of the filling.
Bake for 20-25 minutes until the mushrooms are tender and the topping is golden brown and set.