Prepare the Mushrooms

1. Start by cleaning the mushrooms. Wipe them with a damp cloth to remove any dirt. Avoid washing them under water.
2. Next, carefully remove the stems and set them aside. They will be used in the stuffing, so don’t discard them.
3. Chop the mushroom stems finely. In a skillet, heat 1 tablespoon of olive oil over medium heat. 
4. Add the chopped mushroom stems, onion, and garlic. Saute for around 5 min.
5. Add the chopped spinach to the skillet. Stir for another 2-3 min.

Mixing the filling

1. In a large mixing bowl, combine the softened cream cheese, sautéed mushroom stem mixture, Parmesan cheese, breadcrumbs, dried oregano, salt, black pepper, and red pepper flakes (if using). 
2. Preheat your oven to 375°F (190°C). 
3. Using a small spoon or a piping bag, fill each mushroom cap with the cream cheese and spinach mixture. 
4. Place the stuffed mushrooms on a baking sheet. Drizzle with a bit of olive oil.
5. Bake in the preheated oven for 20–25 minutes, or until the mushrooms are tender and the tops are golden brown