In a skillet, heat olive oil over medium heat. Add minced garlic and sauté for about 1 minute until fragrant.
Add the chopped spinach and cook until wilted. Remove from heat and let cool slightly.
In a bowl, combine the cooked spinach, cream cheese, feta cheese, Parmesan cheese, oregano, salt, and pepper. Mix until well combined.
Stuff the Mushrooms:
Using a spoon, fill each mushroom cap with the spinach and cheese mixture, packing it in lightly.
Bake the Mushrooms:
Place the stuffed mushrooms on a baking sheet lined with parchment paper. Bake for 20-25 minutes, or until the mushrooms are tender and the tops are golden brown.
Garnish and Serve:
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley before serving.