Gently wipe any dirt off the mushrooms with a paper towel or dish towel.

Remove the stems from the mushrooms. Cut off and discard the tough tips and finely chop the stems.

Heat a skillet over medium heat. Add 2 tablespoons of olive oil.

Add the onion, garlic, chopped mushroom stems, and parsley to the skillet with a pinch of salt. Cook until ingredients are softened, stirring occasionally, about 5-7 minutes.

In a medium bowl, mix the sautéed mushroom mixture with the breadcrumbs, parmesan cheese, oregano, and salt and pepper to taste.

Place the mushrooms in a baking dish. Stuff them with the mixture, pressing down to get as much as possible.

Drizzle the remaining two tablespoons of olive oil on top of the stuffed mushrooms.

Cover the baking sheet with foil.

Bake at 375°F degrees for 20 minutes. Remove foil and bake 10-15 more minutes, until mushrooms are golden and bubbling.