Preheat the oven to 375°F (190°C)
Clean the mushrooms and remove the stems
Finely chop the stems
Heat oil or butter in a skillet
Cook chopped stems with garlic and onion until softened
Add breadcrumbs, cheese, herbs, salt, and pepper
Mix until combined
Fill each mushroom cap with the stuffing
Place the stuffed mushrooms on a baking sheet
Drizzle or brush with oil or melted butter
Bake for 15 to 20 minutes
Serve warm