Preheat the oven to 200ºC, fan 180ºC, gas 6. Pull the stalks from each mushroom. Finely chop the stalks and place them in a bowl with the butter, garlic and parsley. Season lightly with black pepper and mix the ingredients together. Divide between the four mushrooms, pressing the butter into each.
Dip each filled mushroom in egg white and then the crumbs, making sure they are thoroughly coated.
Place the coated mushrooms on a baking tray, sprinkling with any leftover crumbs and spray with the oil.
Bake for 20 minutes or until crisp and golden. Serve on a few salad leaves with lime wedges.