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

Remove the stems from the baby bella mushrooms and finely chop them.

Melt a tablespoon of butter in a skillet over medium heat. Add chopped mushroom stems and sauté for about 5 minutes.

Add chopped onion, minced garlic, salt, and pepper; cook until onions soften, about 1-2 minutes.

Combine sautéed mixture with cream cheese, parmesan, parsley, and pecans in a mixing bowl.

Generously fill each mushroom cap with the cheese mixture and sprinkle with reserved parmesan and pecans.

Place stuffed mushrooms on the baking sheet and bake for 20-25 minutes until golden and tender.

Allow to cool slightly and garnish with chopped parsley before serving.