Preheat oven to 200°C. Line a baking tray with baking paper. Cut stems from mushrooms and set aside. Place mushrooms on tray, cup side facing up. Spray with oil.
Place spinach into a bowl and cover with boiling water. Leave for 2 minutes until softened. Drain well. Finely chop spinach and mushroom stems. Mix spinach with mushroom, ricotta, parmesan and parsley. Season with salt and pepper. Spoon into mushrooms. Top with breadcrumbs. Spray with oil. Bake for 15 minutes or until golden.
Meanwhile, toast bread. Top with baked mushrooms and serve.