Just put in chopped onion and chopped shimeji mushrooms. Add half teaspoon olive oil and then top with chopped (bega) extra tasty cheese. Finally pour in the egg mixture (I used 2 eggs and 1 tbsp fresh milk with pinch of baking powder* and dash of pepper). Bake under preheated oven of 180 degree celcius for 20 minutes.
*can be omitted
^ yields me four baked cheese and onion egg
How it looks like before going into oven: