Preheat your oven to 375°F (190°C) and prepare a baking sheet by lightly greasing it with olive oil or parchment paper.

Gently clean the Portobello mushrooms with a damp cloth, removing any dirt. Brush both sides with olive oil, then season the gill side generously with salt and pepper.

In a large skillet, heat a tablespoon of olive oil over medium heat. Add minced garlic and sauté for about 1 minute until fragrant. Then, add chopped spinach and cook until wilted. Incorporate cherry tomatoes, breadcrumbs, Parmesan cheese, and Italian seasoning, stirring to combine for 3-5 minutes until everything is evenly mixed and heated through.

Take the sautéed filling off the heat and begin stuffing each mushroom cap generously with your savory mixture. Use a spoon to ensure the filling is heaping and well-packed. Once all the caps are filled, sprinkle shredded mozzarella cheese over the top of each mushroom.

Carefully place the stuffed mushrooms on the prepared baking sheet and slide them into the preheated oven. Bake for 15–18 minutes, or until the mushrooms are tender and the cheese is bubbly and golden.

Once out of the oven, allow the Stuffed Portobello Mushrooms to cool slightly before serving. For a fresh touch, sprinkle with chopped basil or parsley.