Turn the temperature on the oven to 350 degrees Fahrenheit (175 degrees Celsius). Prepare a baking sheet by lining it with aluminum foil or parchment paper.
In a medium bowl, thoroughly combine the breadcrumbs, garlic, olive oil, Parmesan cheese, oregano leaves, fresh parsley, salt, and pepper. Mix until everything is evenly distributed.
On the baking sheet that has been prepped, arrange the mushrooms with the gill side facing up. The stuffing should be distributed evenly among the mushrooms, and a light amount of pressure should be used to ensure that it sticks.
Bake in an oven that has been warmed for 20 minutes, or until the food is golden brown and fully done. Prepare and serve either hot or at room temperature. Enjoy!