Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Clean the portobello mushrooms by wiping them with a damp paper towel, then remove the stems and gently scrape out the dark gills with a spoon.
Finely dice the onion and red bell pepper, and mince the garlic clove.
In a medium skillet over medium heat, add the olive oil and sauté the onion and bell pepper until softened, about 4 minutes.
Add the garlic and ground turkey to the skillet, breaking the meat apart with a spatula until it is fully browned and cooked through.
Remove the skillet from the heat and allow the turkey mixture to cool slightly for 5 minutes.
In a mixing bowl, combine the cooked turkey mixture with the Greek yogurt, chopped parsley, thyme, sea salt, and black pepper until well incorporated.
Place the mushroom caps on the prepared baking sheet, gill-side up, and divide the turkey filling evenly between the two caps.
Bake for 18-20 minutes until the mushrooms are tender and the filling is heated through.
Remove from the oven and drizzle each stuffed mushroom with the balsamic glaze before serving.