Preheat your oven to 375°F (190°C). Clean the mushrooms by wiping them with a damp paper towel and remove the stems.
In a large skillet, heat the olive oil over medium heat. Add the chopped sweet onion and sauté for about 3-4 minutes until translucent. Add minced garlic, dried thyme, and red pepper flakes, cooking for another minute until fragrant.
Increase the heat to medium-high and add the ground chicken or turkey. Season with salt and pepper. Cook until browned and fully cooked, about 5-7 minutes.
Remove from heat and stir in the grated Gruyere cheese and breadcrumbs until well combined.
Fill each mushroom cap generously with the chicken and cheese mixture.
Place the stuffed mushrooms on a baking sheet lined with parchment paper and bake for 20-25 minutes, until tender and golden brown.
Let cool for a minute before serving warm. Enjoy!
