Preheat your oven to 400°F (200°C) and grease a baking sheet with olive oil.

Remove the stems from the mushrooms, finely chop the stems, and set them aside.

In a skillet over medium heat, melt the butter. Add the chopped mushroom stems and sauté for about 5 minutes.

Incorporate the diced onion, minced garlic, salt, and pepper, cooking for an additional 1-2 minutes until the onion is tender.

Transfer the mixture to a bowl and let it cool.

Stir in cream cheese, parmesan cheese, parsley, and chopped pecans until well combined.

Fill each mushroom cap with approximately one tablespoon of the cheesy filling mixture.

Sprinkle the tops with reserved parmesan cheese and pecans.

Bake for about 20-25 minutes until golden brown and the caps feel slightly soft.

Remove from the oven and let cool for a few minutes before serving.