Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Gently wipe the portobello mushroom caps with a damp paper towel to clean them and remove the stems.
Place the mushroom caps gill-side up on the prepared baking sheet.
In a medium skillet, heat the olive oil over medium heat and sauté the minced garlic for about 30 seconds until fragrant.
Add the ground turkey to the skillet, seasoning it with sea salt, black pepper, and dried oregano.
Cook the turkey, breaking it up with a spoon, until it is fully browned and no longer pink.
Stir in the fresh baby spinach and cook for 1 minute until just wilted, then remove the skillet from the heat.
Stir the fresh parsley and lemon zest into the turkey mixture for a bright, fresh finish.
Spoon the turkey and spinach mixture evenly into the two mushroom caps.
Sprinkle the crumbled feta cheese over the top of each stuffed mushroom.
Bake in the oven for 15 to 18 minutes until the mushrooms are tender and the cheese is lightly golden.