Heat the oven to 180° top-bottom heat. Line a baking tray with baking paper.
Clean the mushrooms and remove the stems. Spread the mushroom heads on the baking tray. The hollow side faces up. Leave them in the oven for about 5 minutes.
Chop garlic and onion, fry them in olive oil. Add the spinach, stir and wait until it collapses. Season with salt and pepper. Squeeze out the water. To do this, put the spinach in a sieve and squeeze out the water with a spoon.
Mix spinach, cream cheese, Emmental cheese and the bell pepper pieces in a bowl. Add salt and pepper and taste.
Take the mushrooms out of the oven, fill the cream cheese mixture into the mushrooms. Put them in the oven. After about 4 minutes, the cream cheese should have a light colors and the Emmentaler should be melted.
Stuffed mushrooms taste really delicious if you sprinkle fresh parsley on them before serving.