Preheat your oven to 400°F and line a rimmed baking sheet with parchment paper.
Clean the portobello mushroom caps with a damp paper towel and carefully remove the stems and dark gills using a spoon.
In a large skillet over medium heat, add the olive oil and ground turkey, breaking it apart with a spatula until fully browned.
Add the minced garlic, sea salt, black pepper, thyme, and rosemary to the skillet and sauté for 2 minutes until fragrant.
Stir in the fresh spinach and cook for 1 minute until just wilted, then remove the skillet from the heat.
Place the mushroom caps on the prepared baking sheet, gill-side up, and fill each cap generously with the turkey and spinach mixture.
Top each mushroom with the crumbled goat cheese, pressing it slightly into the filling.
Bake for 15 to 20 minutes until the mushrooms are tender and the goat cheese is softened and golden.