Preheat your oven to 350°F (175°C).

Remove the stems from the mushroom caps and mince them finely.

Melt butter in a skillet over medium heat, add minced mushroom stems, onion, and thyme. Sauté for 5-7 minutes.

Combine panko breadcrumbs, Parmesan cheese, and parsley in a bowl for the topping.

Mix cooled sautéed mixture with Boursin cheese and half of the breadcrumb mixture.

Brush mushroom caps with olive oil and fill them with the Boursin mixture.

Coat stuffed mushrooms with the remaining panko mixture.

Arrange on a baking sheet and bake for 20 minutes until tender and golden brown.