Preheat your oven to 400°F and line a rimmed baking sheet with parchment paper.
Clean the Portobello mushrooms with a damp cloth, remove the stems, and gently scoop out the gills with a spoon.
Brush the outside and edges of the mushroom caps with the extra virgin olive oil and sprinkle with a pinch of sea salt and black pepper.
Place the mushrooms gill-side down on the baking sheet and roast for 10 minutes to release excess moisture.
While the mushrooms roast, heat a non-stick skillet over medium-high heat and add the ground turkey.
Season the turkey with the remaining sea salt, black pepper, and red pepper flakes, then add the minced garlic.
Cook the turkey until browned and fully cooked through, then stir in the fresh baby spinach until it is just wilted.
Remove the mushrooms from the oven, flip them over, and fill each cap generously with the turkey and spinach mixture.
Crumble the goat cheese over the top of the filling and return the mushrooms to the oven for 5 to 8 minutes until the cheese is soft.
Drizzle each stuffed mushroom with balsamic glaze and serve immediately while hot.