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 use a spoon to gently scrape out the dark gills.
Finely dice the mushroom stems and set aside; discard the gills.
Heat the olive oil in a large skillet over medium heat and add the minced garlic, diced red pepper, and chopped mushroom stems.
Add the ground turkey to the skillet, seasoning with sea salt, black pepper, and dried oregano.
Cook the turkey, breaking it up with a spatula, until it is completely browned and cooked through.
Stir in the fresh spinach and lemon juice, cooking for 1-2 minutes until the greens are just wilted.
Place the mushroom caps on the prepared baking sheet, cavity side up, and fill them generously with the turkey mixture.
Bake for 15-20 minutes until the mushrooms are tender and the filling is slightly golden on top.
Garnish with freshly chopped parsley and serve immediately.