Preheat the oven to 375°F (190°C).
Clean the mushrooms with a damp paper towel and remove the stems.
In a mixing bowl, combine the Boursin cheese, breadcrumbs, Parmesan cheese, parsley, olive oil, garlic powder, black pepper, and salt. Mix until well combined.
Stuff each mushroom cap generously with the cheese mixture.
Place the stuffed mushrooms on a baking sheet lined with parchment paper.
Bake in the preheated oven for 20-25 minutes, or until the mushrooms are tender and the tops are golden brown.
Remove from the oven and let cool for a few minutes before serving.