Follow these simple steps to prepare your delicious Stuffed Portobello Mushrooms:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Prepare the Mushrooms: Clean the mushrooms by gently wiping them with a damp cloth. Remove the stems and gills using a spoon, creating space for stuffing.
3. Make the Filling: In a skillet, heat the olive oil over medium heat. Sauté the onions and garlic for 2-3 minutes until softened. Add the diced bell peppers and cook for an additional 5 minutes.
4. Combine Ingredients: In a bowl, mix the sautéed vegetables with breadcrumbs, cheese, parsley, balsamic vinegar, Italian seasoning, salt, and pepper. Ensure the mixture is well combined.
5. Stuff the Mushrooms: Spoon the filling into each mushroom cap, pressing it down lightly to ensure they are filled generously.
6. Bake: Place the stuffed mushrooms on a baking sheet lined with parchment paper. Bake in the preheated oven for 25-30 minutes or until the mushrooms are tender and the tops are golden brown.
7. Serve: Remove from the oven and let the mushrooms cool for a few minutes before serving. Enjoy these delicious goodies warm!