• Preheat the oven to 390°F (200 °C).

PREPARE THE MUSHROOMS

• Gently pop off the mushrooms' stems. Set aside the stems for later use. Use a damp paper towel to brush off the dirt on the mushroom tops. Don’t rinse them in water. Season with salt and pepper.
• Arrange the clean mushrooms on a parchment-lined baking sheet.

PREPARE THE VEGGIES

• Finely chop the mushroom stems. In a medium skillet over medium-high heat, add olive oil and let it heat up. Stir in the spring onions, the bell pepper, and the mushroom stems. Cook for 3-4 minutes until all veggies are softened. Set aside to cool slightly.

PREPARE THE FILLING

• In a medium bowl, mix the cream cheese, half Gouda and mozzarella cheese, and the cooked veggies. Taste the mixture. It can be already salty to your liking. If not, then add salt. Season with ground black pepper.
• Add the egg and mix well until everything is well blended and creamy.

ASSEMBLE AND BAKE

• Use a spoon to carefully fill the cavity of each mushroom with the filling. Fill just a bit above the top, but don’t overdo it—keeping it neat will make them look their best.
• Top with the remaining grated gouda-mozzarella cheese. Gently press to form a crust. Place the mushrooms in the baking dish, cheese-side up.
• Bake for 15 minutes, until the tops are puffed and golden. Garnish with the green part of spring onions, or/and fresh/dried oregano, thyme, and basil. Serve immediately.