Preheat your oven to 375°F (190°C). This ensures that the mushrooms will cook evenly and the filling will be heated through.

Clean the portobello mushrooms with a damp cloth to remove any dirt. Remove the stems and gently scrape out the gills with a spoon to create space for the filling.

Place the mushrooms, cap side up, on a baking sheet lined with parchment paper.

In a skillet, heat 1 tablespoon of olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant. This step enhances the flavor of the filling.

Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Stir occasionally to ensure even cooking.

In a mixing bowl, combine the sautéed spinach and garlic, softened cream cheese, shredded mozzarella, grated Parmesan, dried oregano, dried thyme, salt, and pepper. Mix until well combined. This mixture will be the flavorful filling for the mushrooms.

Spoon the filling generously into each portobello mushroom cap, pressing down slightly to pack it in. This ensures that each bite is full of flavor.

In a small bowl, mix together the breadcrumbs and additional grated Parmesan. Sprinkle this mixture evenly over the stuffed mushrooms for added texture.

Drizzle a little olive oil over the breadcrumbs to help them brown in the oven.

Bake the stuffed mushrooms in the preheated oven for 20-25 minutes, or until the mushrooms are tender and the topping is golden brown. This step allows the flavors to meld together and the cheese to melt beautifully.

Remove from the oven and let cool for a few minutes before serving. This helps to avoid burns from hot cheese.