Place mushroom caps on a sheet pan lined with parchment paper, brush each one with a little bit of olive oil.
In a bowl combine sausage, onion and parmesan. mix with your hands to combine. Stuff a heaping mound of sausage into each mushroom cap.
Place stuffed mushrooms in a 350 degree F, pre-heated oven. Bake about 25 minutes until sausage is cooked through.
Drizzle with a bit of olive oil and garnish with freshly grated parmesan and herbs.
Makes 18 stuffed mushrooms