01 - Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
02 - Gently clean the Portobello mushroom caps with a damp paper towel. Carefully remove the stems and the dark gills from inside the caps using a spoon. Brush both the inside and outside of the mushroom caps with 2 tablespoons of olive oil and season generously with salt and freshly ground black pepper. Arrange the prepared caps, gill side up, on the lined baking sheet.
03 - In a medium mixing bowl, combine the shredded mozzarella cheese, ½ cup grated Parmesan cheese, softened cream cheese, chopped fresh parsley, minced garlic, dried oregano, dried thyme, and breadcrumbs. Stir until all ingredients are thoroughly blended into a cohesive filling.
04 - Evenly distribute the prepared cheese filling into each of the prepared mushroom caps. Gently press the filling down to ensure it's well-packed.
05 - Drizzle the filled mushroom caps with 1 tablespoon of olive oil. Sprinkle the tops with the remaining 2 tablespoons of grated Parmesan cheese. If desired, add the optional chopped fresh parsley for an extra touch of green.
06 - Place the baking sheet in the preheated oven and bake for 22 to 25 minutes. The mushrooms should become tender, and the cheese topping should be golden brown and delightfully bubbly.
07 - Remove from the oven and serve the stuffed Portobello mushrooms hot. They make an excellent appetizer or can be served with a side salad as a satisfying vegetarian main course.