Clean the mushrooms and remove the stems. Set them aside on a baking sheet.
Heat olive oil in a pan over medium heat. Add the diced onion and garlic and sauté until fragrant, about 3 minutes.
Add the cooked quinoa to the pan with the onions and garlic. Stir in parsley, thyme, salt, and pepper. Cook for another 2 minutes until the quinoa absorbs the flavors.
Spoon the quinoa mixture into each mushroom cap, pressing gently to pack it in. Top each mushroom with cheese.
Bake for 20-25 minutes, or until the mushrooms are tender and the cheese is melted and bubbly.
Optional: For a golden-brown top, broil the mushrooms for 2 minutes at the end.
Serve warm and enjoy!
Notes
Feel free to customize the stuffing with other vegetables or protein options.
If the mushrooms release too much moisture, bake them upside down to allow the liquid to evaporate.