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 use a spoon to gently scrape out the dark gills.
Brush the outside of the mushroom caps with 0.5 tbsp of olive oil and place them gill-side up on the prepared baking sheet.
Mince the garlic and finely chop the fresh rosemary and thyme.
In a medium skillet, heat the remaining 0.5 tbsp of olive oil over medium heat. Add the minced garlic and sauté for 1 minute until fragrant.
Add the ground turkey to the skillet, breaking it up with a spatula. Season with sea salt, black pepper, rosemary, and thyme.
Once the turkey is nearly browned, add the fresh spinach to the skillet and stir until just wilted.
Divide the turkey and spinach mixture evenly between the two mushroom caps, pressing down slightly to pack the filling.
Roast the stuffed mushrooms in the oven for 15 to 20 minutes, or until the mushrooms are tender and the filling is golden.
Remove from the oven and drizzle each mushroom with the balsamic glaze before serving warm.