Preheat oven to 180°C fan forced.
Prepare mushrooms: Gently remove the stems from the mushrooms and scoop out the mushroom flesh. Finely chop the removed stems and flesh.
Make the filling: In a bowl, mix the chopped mushroom stems with ricotta, parsley, mozzarella, spinach, and a pinch of salt until well combined.
Stuff the mushrooms: Fill each mushroom generously with the ricotta mixture.
Add topping: Sprinkle garlic and herb breadcrumbs and grated parmesan cheese over each filled mushroom.
Bake in oven: Place mushrooms on a lined baking tray and bake for 20–25 minutes, or until golden and cooked throug
Crisp the pancetta: While the mushrooms are cooking, pan-fry pancetta slices over medium heat until crispy. Transfer to a paper towel to drain excess fat.
Serve: Top each stuffed mushroom with crispy pancetta and enjoy warm.