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.
Finely mince the garlic and chop the fresh spinach and mushroom stems.
Heat the olive oil in a skillet over medium heat, then add the ground turkey, minced garlic, and chopped mushroom stems.
Cook the turkey until browned and fully cooked through, breaking it into small crumbles with a spatula.
Stir in the fresh spinach, sea salt, black pepper, and fresh thyme, sautéing until the spinach is wilted.
Place the mushroom caps on the prepared baking sheet, cavity side up, and fill each generously with the turkey and spinach mixture.
Top each stuffed mushroom with grated parmesan cheese and bake for 15 to 20 minutes until the mushrooms are tender.
Remove from the oven and finish with a drizzle of balsamic glaze before serving hot.