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 gills with a spoon.
In a large skillet over medium-high heat, add the olive oil and ground turkey, breaking it up as it cooks until browned and no longer pink.
Add the minced garlic, sea salt, and black pepper to the skillet, sautéing for 1 minute until fragrant.
Stir in the chopped spinach and cook until just wilted, then remove the skillet from the heat.
Mix in the fresh parsley, lemon zest, and lemon juice to the turkey mixture for a bright finish.
Place the mushroom caps on the prepared baking sheet and divide the turkey stuffing evenly among 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.