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 scrape out the gills with a spoon.
Finely mince the garlic and roughly chop the fresh spinach, oregano, and thyme.
Heat the extra virgin olive oil in a skillet over medium heat and add the ground turkey, cooking until browned and crumbled.
Stir in the minced garlic, sea salt, black pepper, oregano, and thyme, sautéing for 1 minute until fragrant.
Add the chopped spinach to the skillet and cook until just wilted, then remove from heat.
Place the mushroom caps on the baking sheet, gill-side up, and divide the turkey mixture evenly between them.
Sprinkle the crumbled feta cheese over the top of each stuffed mushroom.
Bake for 15 to 20 minutes until the mushrooms are tender and the cheese is slightly golden.