Preheat oven to 180 degrees Celsius

Remove stalks using a spoon or knife from mushrooms and cut up the stalk

Finely chop onion, and add garlic to saute in olive oil for 3 minutes or until onions become slightly translucent. Add the cut up mushroom stalks

Roughly chop rinsed spinach and add to pan. Place lid on pan. Stir occasionally. Season with oreganum and pepper

Once spinach is cooked, remove from heat. Crumb the feta into the mixture (add olives/ sundried tomatoes - optional)

Place mushrooms on an oven tray and cook for about 5 - 7 minutes or until the mushroom sweats and there is liquid inside the mushroom

Remove mushrooms from oven and drain liquid from mushrooms

Fill mushrooms with spinach feta mixture and add grated cheese on top

Bake till cheese slightly browns